This cake, which is adapted from Martha Stewart, is so good you’ll be hard-pressed not to eat the whole thing in one sitting.
3 1/2 tablespoons unsalted butter, room temperature, divided
1/2 cup plus 1 tablespoon flour, divided
2 tablespoons whole-wheat flour
1/4 teaspoon baking powder
1/4 teaspoon baking soda
Pinch of salt
1/4 cup sugar
1 egg, beaten
1/4 teaspoon vanilla extract
1/4 cup plus 2 1/2 tablespoons sour cream
3/4 cup fresh blueberries
2 tablespoons flour
2 tablespoons light brown sugar
1/4 teaspoon ground cinnamon
2 tablespoons cold unsalted butter
1. Butter a 12-ounce ramekin with 1 tablespoon butter and place on a baking sheet. Set aside.
2. Preheat oven to 350°F.
3. In a medium bowl, whisk together 1/2 cup flour, whole-wheat flour, baking powder, baking soda and salt.
4. Using an electric mixer fitted with paddle attachment, cream remaining 2 1/2 tablespoons butter and sugar on medium-high speed until light and fluffy. Add 3/4 egg (discard extra egg or save for later use) and vanilla and mix again.
5. Slowly add flour mixture, until just combined. Add sour cream and mix again.
6. In a small bowl, toss remaining 1 tablespoon flour with blueberries and gently fold into mixture. Do not overmix. Transfer batter to prepared ramekin.
7. In another small bowl, make crumb topping. Combine flour, sugar and cinnamon. Cut in butter with a fork until coarse crumbs form. Sprinkle on top of cake and bake until a toothpick comes out clean, about 40-45 minutes. Serve warm or at room temperature.