Gluten Free Rhubarb Coffee Cake (Rhabarber Streuselkuchen)

This Gluten Free Rhubarb Coffee cake is one of those delightful spring desserts that hits all the right notes. Picture a tender gluten free vanilla cake topped with tangy, juicy rhubarb and a generous layer of sweet, crunchy streusel. The contrast between the tart rhubarb and the sugary topping is simply perfect.

Rhabarber Streuselkuchen makes the perfect breakfast cake or a little something-something to serve for "Kaffee & Kuchen" (Mid Afternoon Coffee Break).

Recipe Ingredient Notes

Gluten Free Flour: I have tested this Gluten Free Rhubarb Coffee Cake recipe with Bob's Red Mill 1-1 and King Arthur Measure for Measure. Both of these blends yielded a tender, moist crumb and worked well in this application. I did prefer the cake made with the King Arthur gluten free flour blend. It was more tender and stayed fresh longer. It's worth noting that while I haven't tried other brands of flour in this recipe, it doesn't necessarily mean that they won't work.

Almond Flour: The almond flour gives this Rhabarber Streuselkuchen its beautiful structure and moist crumb. If you prefer to keep this recipe nut-free, please substitute the almond flour with the same amount of gluten-free flour. You can also substitute the almond flour with hazelnut flour or walnut flour.

Rhubarb: When you're picking out rhubarb for baking, go for stalks that are firm, crisp, and have a nice bright color. Make sure they look glossy and don’t have any blemishes. You can usually find rhubarb in the produce section of your grocery store or at a farmer's market. And if you're really lucky, you might even have some growing in your own backyard.

Milk: My aunt's original Rhabarber Streuselkuchen recipe is made with water. I use low-fat milk but feel free to use dairy milk (any percentage), nondairy milk, or even water. Just remember that cake made with water or nondairy milk will brown less.

Vanilla Extract/Vanilla Paste: Vanillezucker, a vanilla-flavored sugar, is commonly used in German-speaking countries. It may be challenging to find in American grocery stores but if you have a European Grocery Store near by, make sure to check their baking aisle. Use Vanilla Paste or Vanilla Extract as a substitute for Vanillezucker.

Tools needed to make a Rhabarber Streuselkuchen

I use a 9 x 13inch baking pan to make this cake. It gives the cake the perfect thickness. You can also use a  jelly roll pan to make this Austrian Streuselkuchen. Remember if you use a jelly roll pan the cake will be thinner and bake a lot faster. Baking Times will depend on the size of the pan one uses.

You will also need a mixer (electric hand mixer or stand mixer for the egg whites), a large mixing bowl and two small mixing bowls, a flexible rubber spatula, an offset knife, a pairing knife, and a sifter.

Brown Sugar Streusel

It's no secret that I love a good streusel topping for my coffee cakes. This Streusel is made with melted butter or if you like you may use brown butter instead. If you never made brown butter before, you can find detailed instructions on how to make brown butter in this blog post: How to make Brown Butter. You can also replace some with of the gluten free flour with gluten free oats or some nuts such as walnuts, pecans, or almonds. Rhubarb and Almonds especially pair very well.

1. Melt the butter in a small pot on the stove or a microwave safe bowl. Allow to cool for a few minutes.
2. In the meantime combine the Gluten Free Flour, light brown sugar, ground ginger (or ground cinnamon), and kosher salt in a mixing bowl and whisk together.
3. Using a fork or a small spatula, lightly mix the dry ingredients and the melted butter together until crumbles form. Don’t overmix.
4. Place the brown sugar streusel in the fridge while you prepare the gluten free cake batter for the Rhubarb Coffee Cake. You may even freeze the crumb topping for up to 3 months.

Prepare Rhubarb for the Coffee Cake

I like to toss the sliced rhubarb with some gluten free flour before using it to top the coffee cake. Rhubarb has a lot of moisture and this reduces the chances of the cake to become soggy within a day or two.

1. Wash the rhubarb stalks under cold water and dry them with a paper towel. Remove both ends and any leaves as they are toxic.
2. Slice the rhubarb stalks into rounds around ¼" wide round slices (kinda like cutting celery) and add them to a mixing bowl. If the stalks are particularly thick, you might want to cut them lengthwise first and then into smaller pieces to ensure even cooking.
3. Add the sliced rhubarb to a small bowl, add the gluten free flour, and stir to combine making sure the fruit is coated with the flour. Don't add the raspberries since they don't have to be coated in flour.
4. Set the fruit aside while you prepare the rhubarb coffee cake batter.

Rhubarb Coffee Cake Batter

This rhubarb coffee cake comes together in no time. You will need two mixing bowls - one to whisk the egg whites and one to whisk the wet ingredients. I use a hand mixer for the egg whites and a bowl and a whisk for everything else.

1. Preheat the oven to 350F. Spray the 9x13 baking pan with cooking spray and line it with parchment paper and set it aside.
2. In a small bowl combine the gluten free flour, almond flour, kosher salt, and baking powder. You can either whisk or sift the dry ingredients together. Just make sure they are fully combined and there are no clumps.
3. To a mixing bowl add the granulated sugar and the lemon zest. Remember to reserve 20 grams of sugar for the egg whites. With the back of a spoon or clean hands rub the zest into the sugar. This brings out the lemon flavor and will give the coffee cake a subtle hint of lemon.
4. Carefully separate the eggs. Add the egg yolks to the bowl with the lemon sugar and place the 4 egg whites in a clean, separate mixing bowl. Set the egg whites aside.

5. Whisk the lemon sugar and egg yolks together until lighter in color and doubled in volume. At first, the mixture will thicken up but if you keep whisking it will turn into a smooth liquid.
6. Add the oil and milk (or water) to the egg yolk mixture and whisk until smooth. Set aside while you whisk the egg whites. During my recipe testing I realized if I add the dry ingredients to the wet ingredients at this point, the batter will become very stiff making it almost impossible to fold in the egg whites. Therefore I recommend adding the dry ingredients to the wet ingredients once you whisked the egg whites.

5. With an electric hand mixer (or stand mixer) whisk the egg whites with a pinch of salt until they appear frothy. Add the reserved granulated sugar little by little and mix until the egg whites appear glossy and shiny. The egg whites should be soft/medium stiff. Overmixed egg whites appear dull and dry.
6. Add the dry ingredients to the wet ingredients in two parts. Whisk the ingredients together until the batter is smooth.
7. To the batter, add about ⅓ of the beaten egg whites and fold them in gently. This will help to loosen up the batter. Then, add the remaining egg whites and fold them in carefully until the rhubarb coffee cake batter becomes light and airy. Make sure to be gentle and not overmix the batter.

Baking Instructions

Ensure your oven is preheated to 350F, and the rhubarb and the streusel topping are prepared.

1. Transfer the gluten free rhubarb cake batter to the prepared baking dish. With a small offset knife or the back of a spoon, spread it out evenly.
2. Sprinkle the cake in an even layer with the prepared rhubarb and raspberries. There is no need to press the fruit into the batter.
3. Top the Rhabarber Streuselkuchen with the prepared brown sugar streusel. It's okay if some of the fruit peaks through.
4. Bake the Gluten Free Rhubarb Coffee Cake at 350F for 34-38 minutes. The cake will be golden brown and a cake tester or toothpick insert in the center comes out clean. If you prefer using a digital thermometer, ensure the internal temperature in the center of the cake is above 200F.
5. Remove the coffee cake from the oven and place it on a cooling rack. Allow for it to cool in the pan for at least 15-20 minutes before serving.
   

Serving Idea

This cake can be tricky to remove from the pan so I choose to serve it right from the pan. I love serving this Gluten Free Rhubarb Coffee Cake Serving still slightly warm from the oven. Dust the cake with some powdered sugar and if you like, top each slice with a generous dollop of freshly whipped cream or a scoop of vanilla ice cream.

Storage & Freezing

Although this Rhabarber Streuselkuchen is delicious the day it was baked, it is delightful the next day. Cake made with Rhubarb tends to be moist, and as it sits, the moisture distributes more evenly throughout the cake. This can prevent dryness and create a more consistently moist texture. To store any leftovers, keep them in an airtight container at room temperature for 3-4 days.

To freeze pieces of the cake, make sure it is completely cool. Freeze individual pieces in an airtight container for up to 2 months. Thaw at room temperature.

FAQ - Gluten Free Rhubarb Coffee Cake