Rhubarb Coffee Cake with Buttery Crumb Topping

Rhubarb coffee cake pairs a soft sour cream crumb with tart bites of rhubarb, all under a thick cinnamon streusel that turns crisp and buttery in the oven. It bakes in a 9-inch square pan and cuts into 9 generous squares, which suits a spring brunch table or an afternoon coffee break.

Ingredients

For the Cake

• 2 cups all-purpose flour
• 1 teaspoon baking powder
• 1/2 teaspoon baking soda
• 1/2 teaspoon salt
• 1/2 cup unsalted butter, softened
• 3/4 cup granulated sugar
• 2 large eggs
• 1 teaspoon vanilla extract
• 1 cup sour cream
• 2 cups chopped rhubarb, cut into small pieces

For the Crumb Topping

• 3/4 cup all-purpose flour
• 1/2 cup brown sugar
• 1 teaspoon cinnamon
• 1/4 teaspoon salt
• 6 tablespoons cold unsalted butter, cubed

Cut the rhubarb into small, even pieces so it softens fully while the cake bakes. If the stalks are especially thick or stringy, trim away the outer fibers so the texture stays tender.

How to Make Rhubarb Coffee Cake

1. Preheat the oven to 350°F and grease a 9-inch square baking pan. Line the bottom with parchment if you want especially clean slices.
2. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt until evenly combined.
3. In a separate bowl, mix the crumb topping ingredients with a fork or pastry cutter until the mixture forms chunky crumbs with some pea-sized butter pieces still visible. Refrigerate while you prepare the batter so the topping stays crisp during baking.
4. Beat the butter and sugar until the mixture looks pale and fluffy, about 2 to 3 minutes. Add the eggs one at a time, then stir in the vanilla extract.
5. Mix in half of the dry ingredients, followed by the sour cream, then the remaining dry ingredients. The batter should look thick and smooth without dry streaks.
6. Fold in the chopped rhubarb gently so the pieces stay evenly distributed throughout the batter.
7. Spread the batter into the prepared pan and smooth the top with a spatula. Sprinkle the crumb topping evenly over the surface, lightly pressing larger clumps into place.
8. Bake for 40 to 50 minutes, or until the top is golden brown and the center springs back lightly when touched. A toothpick inserted near the middle should come out with a few moist crumbs but no wet batter.
9. Let the cake cool for at least 20 minutes before slicing. The crumb topping firms up as it cools, making cleaner slices easier.

Why Sour Cream and a Thick Crumb Work With Rhubarb

Sour cream keeps the cake moist and gives the batter enough structure to hold juicy fruit without turning gummy, and its tang works with rhubarb’s sharpness. The oversized crumb topping adds a crunchy contrast to the soft cake underneath and helps balance the tartness.

Keeping the Crumb Topping Crisp and the Center Fluffy

• **Keep the topping cold.** If the butter gets warm before baking, the crumbs melt into the cake instead of staying defined. Chilling the crumb mixture while you make the batter prevents that.
• **Leave some pea-sized butter pieces** in the crumbs and press larger clumps in lightly, so you get a rough, bakery-style top.
• **Thaw and drain frozen rhubarb.** Frozen rhubarb releases extra moisture as it bakes, and too much liquid makes the center dense instead of fluffy.
• **Fold, don’t stir,** once the rhubarb goes in, so the pieces stay spread through the batter.

Variations and Substitutions

• **Strawberry rhubarb:** replace 1 cup of the rhubarb with chopped strawberries. The berries soften the tartness and add moisture, so expect a slightly softer crumb.
• **Nuts:** add chopped pecans or walnuts to the streusel for extra crunch.
• **Orange zest** in the batter brightens the flavor without overpowering the rhubarb.
• **Greek yogurt for sour cream:** plain full-fat Greek yogurt gives a similar texture and tang. Avoid fat-free, which can make the cake less tender.

Storing Rhubarb Coffee Cake

Keep leftover slices tightly covered at room temperature for up to 2 days, or refrigerate for up to 5 days. Warm individual slices for about 10 seconds in the microwave to soften the crumb. The flavor is often better the next morning as the rhubarb settles into the crumb.

More Rhubarb Recipes to Bake

If you have a rhubarb haul to use up, try the rhubarb muffins with brown sugar streusel for grab-and-go mornings, or the strawberry rhubarb crisp for dessert. A spoonful of rhubarb sauce also works well over a warm slice.

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