Ingredients

• 1/3 cup granulated sugar
• 1/4 cup all-purpose flour
• 1/4 cup rye flour
• 3 tablespoons cacao nibs
• 2 tablespoons unsweetened cocoa powder
• 1/4 teaspoon kosher salt
• 1/4 cup chilled unsalted butter, cut into pieces
• Nonstick vegetable oil spray
• 3/4 cup all-purpose flour
• 3/4 cup rye flour
• 1/2 cup unsweetened cocoa powder
• 1 teaspoon baking powder
• 3/4 teaspoon baking soda
• 3/4 teaspoon kosher salt
• 3/4 cup (1 1/2 sticks) unsalted butter, room temperature
• 1/2 cup granulated sugar
• 1/3 cup (packed) light brown sugar
• 2 large eggs
• 1 teaspoon vanilla extract
• 3/4 cup buttermilk
• 1/4 cup plain whole-milk Greek yogurt

Instructions

1. Whisk granulated sugar, all-purpose flour, rye flour, cacao nibs, cocoa powder, and salt in a medium bowl until blended. Work in butter with your fingers to form large clumps.there should be no dry spots. Cover and chill.
2. Do ahead: Crumble can be made 2 days ahead. Keep chilled.
3. Cake and assembly: Preheat oven to 350°. Coat a 9"-diameter cake pan with nonstick spray and line with a parchment round. Whisk all-purpose flour, rye flour, cocoa powder, baking powder, baking soda, and salt in a medium bowl. Using an electric mixer on mediumhigh speed, beat butter, granulated sugar, and brown sugar in a medium bowl until light and fluffy, about 5 minutes. Scrape down sides of bowl and add eggs and vanilla; mix until blended, about 2 minutes. Reduce speed to low and add half of dry ingredients followed by buttermilk, mixing well after each addition. Repeat with remaining dry ingredients and yogurt (this is a stiffer batter). Scrape into prepared pan. Scatter crumble over. Bake, rotating once, until cake starts to pull away from sides of pan and a tester inserted into the center comes out clean, 60-70 minutes. Let cake cool in pan on a wire rack before turning out. Do ahead: Cake can be made 3 days ahead. Store tightly wrapped at room temperature.
4. Preheat oven to 350°. Coat a 9"-diameter cake pan with nonstick spray and line with a parchment round. Whisk all-purpose flour, rye flour, cocoa powder, baking powder, baking soda, and salt in a medium bowl.
5. Using an electric mixer on mediumhigh speed, beat butter, granulated sugar, and brown sugar in a medium bowl until light and fluffy, about 5 minutes. Scrape down sides of bowl and add eggs and vanilla; mix until blended, about 2 minutes. Reduce speed to low and add half of dry ingredients followed by buttermilk, mixing well after each addition. Repeat with remaining dry ingredients and yogurt (this is a stiffer batter). Scrape into prepared pan. Scatter crumble over.
6. Bake, rotating once, until cake starts to pull away from sides of pan and a tester inserted into the center comes out clean, 60-70 minutes. Let cake cool in pan on a wire rack before turning out.
7. Do ahead: Cake can be made 3 days ahead. Store tightly wrapped at room temperature.