1. Preheat oven to 350°.
2. To prepare crumble, combine first 4 ingredients in a bowl, stirring with a whisk. Cut in 2 tablespoons butter using a pastry blender or two knives until mixture resembles coarse meal. Stir in toasted pecans.
3. To prepare cake, weigh or lightly spoon 6.75 ounces flour into dry measuring cups; level with a knife. Combine 6.75 ounces flour and next 4 ingredients (through 1/4 teaspoon salt); stir with a whisk. Place 3 tablespoons butter and granulated sugar in a medium bowl; beat with a mixer at medium speed until well combined. Add whole egg and egg yolk, 1 at a time, beating well after each addition. Add milk, sour cream, and vanilla; beat at low speed for 1 minute or until well combined. Add the flour mixture; beat at low speed 1 minute or just until combined.
4. Spoon half of batter into an 8-inch round metal cake pan coated with baking spray. Sprinkle with half of crumble mixture. Spread remaining batter over crumble, smoothing top with a spatula. Sprinkle evenly with remaining crumble mixture. Bake at 350° for 30 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack for 15 minutes. Place a plate upside down on top of cake; invert onto plate. Place another plate upside down on top of cake; invert onto plate.