Rhubarb Streusel Cake with Warm Vanilla Sauce
This comforting fruit cake combines tart rhubarb, a soft buttermilk crumb, and a crisp, buttery sugar topping. Slices are served with a glossy, warm vanilla sauce for a rich finish.
Equipment
- 9-inch square pan
- stand or hand mixer
- Small saucepan
Ingredients
For the Rhubarb Cake
- 1 cup granulated sugar
- 1 egg
- 2 tablespoons unsalted butter melted
- 1 cup buttermilk
- 1/2 teaspoon salt
- 1/2 teaspoon baking soda
- 1 teaspoon baking powder
- 2 cups flour
- 1 cup diced fresh rhubarb
For the Sugar Topping
- 2 tablespoons unsalted butter melted
- 1/2 cup granulated sugar
For the Vanilla Sauce
- 3/4 cup granulated sugar
- 1/2 cup butter
- 1/2 cup evaporated milk
- 1 teaspoon pure vanilla extract
Instructions
For the Rhubarb Cake
- Heat the oven to 350°F and grease a 9-inch square pan. Coat the bottom and corners well so the fruit-filled cake releases cleanly after baking.
- Beat the sugar, egg, and melted butter in a large bowl with a stand or hand mixer. Continue until the mixture looks smooth and evenly blended.
- Mix in the buttermilk until the batter is uniform. The mixture should look creamy with no streaks of liquid around the bowl.
- Add the salt, baking soda, and baking powder, then stir to distribute them through the batter. Scrape the bowl so the leavening does not collect in one spot.
- Mix in the flour until the batter comes together. Stop once the flour disappears to avoid a tight, tough cake crumb.
- Fold in the diced fresh rhubarb by hand and transfer the batter to the prepared pan. The fruit should be spread throughout the batter rather than gathered in one area.
For the Sugar Topping
- Stir the melted butter and sugar together, then scatter the mixture over the batter. Leave the topping uneven in small patches for a more textured, crackly finish.
- Bake at 350°F for about 40 to 45 minutes. The cake is ready when a tester inserted into the center comes out clean.
For the Vanilla Sauce
- Place the sugar, butter, and evaporated milk in a small saucepan over medium-high heat and stir as the butter melts. The mixture will become smooth and glossy as it warms.
- Bring the sauce to a boil and stir constantly for 1 minute. Butter and vanilla will scent the kitchen, and the sauce should look slightly thicker than when it first heated.
- Take the saucepan off the heat and stir in the vanilla extract. The sauce should lightly coat the back of a spoon and continue thickening a little as it cools.
- Spoon the warm sauce over individual servings of cake. Serve while the sauce flows easily and the topping still has a delicate crunch.
Notes
Moisture control: Pat the diced rhubarb thoroughly dry before folding it into the batter. If the stalks are very juicy, macerate them briefly with some of the measured sugar and drain well to prevent a soggy bottom.
Mixing tip: Stop mixing as soon as the flour disappears, and fold the rhubarb in gently by hand to ensure a tender cake crumb.
Topping tip: Scatter the butter and sugar topping in loose clumps over the batter without pressing it down. This allows it to bake into a lightly crisp, crackly layer.
Sauce fix: Stir the sauce constantly while it boils. If it starts to look grainy or oily from prolonged boiling, remove it from the heat immediately and whisk gently until it comes back together.
Storage: Store the cooled cake at room temperature and keep the vanilla sauce in an airtight container in the refrigerator. Wait to pour the warm sauce over individual slices until serving so the topping stays crisp.
Nutrition information is an estimate based on common ingredients and serving sizes. Values may vary depending on brands, portions, and substitutions.