1/2 pound rhubarb trimmed and sliced 1/2-inch thick
1/4 cup sugar for filling
2 teaspoons cornstarch for filling
1/2 teaspoon ground ginger for filling
1/3 cup dark brown sugar for crumbs
1/3 cup granulated sugar for crumbs
1 teaspoon ground cinnamon for crumbs
1/2 teaspoon ground ginger for crumbs
1/8 teaspoon kosher salt for crumbs
1/2 cup butter (4 ounces or 115 grams) melted, for crumbs
1 3/4 cups cake flour for crumbs
1/3 cup sour cream
1 large egg
1 large egg yolk
2 teaspoons vanilla extract
1 cup cake flour
1/2 cup granulated sugar
1/2 teaspoon baking soda
1/2 teaspoon baking powder
1/4 teaspoon kosher salt
6 tablespoons butter (85 grams) softened, cut into 8 pieces
Equipment
oven
cake pan
large bowl
electric mixer
spatula
toothpick
Directions
Preheat oven to 325 degrees. Grease an 8-inch-square or 9-inch round cake pan.
Make the filling: Toss rhubarb with sugar, cornstarch and ginger, and set aside.
Make the crumbs: In a large bowl, whisk sugars, spices and salt into melted butter until smooth. Then, add flour with a spatula or wooden spoon. Press it into the bottom of the bowl and set it aside.
Make the cake: In a small bowl, stir together the sour cream, egg, egg yolk and vanilla. With an electric mixer on low speed, combine flour, sugar, baking soda, baking powder, and salt.
Gradually add butter and a spoonful of sour cream mixture and mix on medium speed until flour is moistened. Increase speed and beat for 30 seconds.
Add remaining sour cream mixture and beat in thoroughly, then scrape down the sides of the bowl with a spatula.
Scoop out about 1/2 cup batter and set it aside.
Scrape remaining batter into prepared pan. Spoon rhubarb over batter. Dollop set-aside batter over rhubarb; it does not have to be even.
Use your fingers to break the topping mixture into big crumbs, about 1/2 inch to 3/4 inch in size. Make sure most are around that size. Sprinkle over cake.
Bake cake until a toothpick inserted into center comes out clean of batter (it might be moist from rhubarb), 45 to 55 minutes. Cool completely before serving.