Equipment
* optional
Ingredients
Crumb Topping
- 115 g unsalted butter, melted and slightly cooled
- 100 g light brown sugar, packed
- 50 g granulated sugar
- 5 g ground cinnamon
- 2 g salt
- 190 g cake flour
Rhubarb Filling
- 300 g rhubarb, diced into 1 cm pieces
- 65 g granulated sugar
- 8 g cornstarch
- 15 ml lemon juice, freshly squeezed
Cake Batter
- 250 g cake flour
- 4 g baking powder
- 2 g baking soda
- 3 g salt
- 115 g unsalted butter, softened to room temperature
- 150 g granulated sugar
- 2 eggs, room temperature
- 120 g sour cream, room temperature
- 10 ml vanilla extract
Nutrition (per serving)
Method
Preheat your oven to 175°C (350°F). Grease a 23x23 cm (9x9 inch) baking pan and line it with parchment paper, leaving an overhang on the sides for easy removal.
Prepare the crumb topping. In a medium bowl, whisk together the melted butter, brown sugar, granulated sugar, cinnamon, and salt. Add the cake flour and use a fork or your fingers to gently mix until large, cohesive crumbs form. Set aside.
In a separate mixing bowl, whisk together the cake flour, baking powder, baking soda, and salt for the batter.
In a large bowl, use a mixer on medium speed to cream the softened butter and granulated sugar for about 3 minutes, until light and fluffy. Beat in the eggs one at a time, scraping down the bowl between additions, then blend in the vanilla extract.
Reduce the mixer speed to low. Add one-third of the dry ingredients, followed by half of the sour cream. Repeat, ending with the final third of the dry ingredients. Mix only until just combined; the batter will be thick.
Spread slightly more than half of the cake batter evenly into the bottom of the prepared baking pan using an offset spatula.
In a medium bowl, toss the diced rhubarb with the granulated sugar, cornstarch, and lemon juice until well coated. Scatter this filling evenly over the bottom layer of batter.
Drop the remaining cake batter in small spoonfuls over the rhubarb layer. Use the offset spatula to gently spread it as evenly as possible, though it is fine if some rhubarb peaks through. Sprinkle the prepared crumb topping generously and evenly over the top.
Bake in the preheated oven for 45 to 55 minutes. The cake is ready when the crumb topping is deeply golden and a wooden skewer inserted into the center comes out clean or with moist crumbs.
Transfer the baking pan to a wire rack. Allow the coffee cake to cool for at least 1 hour before using the parchment overhang to lift it out of the pan for slicing.
Chef's Notes
- Cake flour is essential here. Its lower protein content interacts beautifully with the sour cream and butter, yielding an incredibly tender, velvety crumb that contrasts sharply with the crunchy topping.
- If your rhubarb stalks are exceptionally thick, slice them in half lengthwise before dicing to ensure they cook down properly within the baking time.
- Using sour cream or buttermilk provides lactic acid, which reacts with the baking soda to give the cake lift, while also tenderizing the gluten strands.
- Do not compress the crumb topping into the batter. Sprinkling it lightly allows the heat to circulate through the streusel, creating a wonderfully crisp, craggy texture.
Storage
Refrigerator: 5 days — Store in an airtight container to prevent the crumb topping from softening too quickly.
Freezer: 3 months — Wrap individual slices tightly in plastic wrap, then place in a freezer-safe bag.
Reheating: Warm individual slices in the microwave for 15 seconds, or in a 150°C (300°F) oven for 5 to 7 minutes to re-crisp the topping.
