This dense, moist cake is a perfect base for its white sugar crumb topping. Watch out when you cut it; in typical crumb cake fashion, the topping will scatter a bit.
Preheat the oven to 325°F. Lightly grease a 9" square cake pan.
In a medium-sized mixing bowl, beat together the butter, sugar, salt, and flavorings for 2 minutes, till smooth.
Add the eggs, beating well after each addition; continue beating after adding the last egg for at least 3 minutes at medium-high speed. The batter should look fluffy, with no grains of sugar visible.
Add the flour and baking soda to the butter mixture, beating gently to combine.
Add the buttermilk/yogurt/sour cream, beating gently until well-blended.
Spread the batter in the prepared pan.
Bake the cake for 30 minutes. While it's baking, prepare the topping.
Mix all of the topping ingredients together just till medium crumbs form. If you mix too long the crumbs will become too large, so pay attention.
After 30 minutes, remove the cake from the oven. Quickly and gently sprinkle the crumbs on top, and return to the oven.
Bake for an additional 15 minutes, until a cake tester inserted into the center comes out clean. Remove the cake form the oven, and cool it completely on a rack.
When the cake is completely cool, dust it with confectioners' sugar.
For a blueberry crumb cake, sprinkle 1 cup (170g) fresh or frozen blueberries atop the batter in the pan before baking.
For more distinct crumbs on top, prepare the topping with 1/4 cup (46g) vegetable shortening and 4 tablespoons (57g) butter, cut in chunks, in place of the 4 tablespoons (57g) melted butter.
Looking for that distinctive "bakery" flavor? When making the cake, reduce the vanilla to 2 teaspoons and add 1/2 teaspoon Buttery Sweet Dough Flavor. In the crumb topping, reduce the vanilla to 1/2 teaspoon and add 1/4 teaspoon Buttery Sweet Dough Flavor. Buttery Sweet Dough Flavor is widely available online.
