Whole grain blueberry buckle

My lab group recently went on a crazyawesome retreat to New Hampshire, and one of the things we did there was blueberry picking at Berry Knoll farm. The blueberries at the farm were some of the best I have ever tasted, and I came home with about a quart of them. I saved half to eat with yogurt and granola for my breakfasts this week, and started looking for a recipe to make with the other half. I decided to make something from Good to the Grain and ended up choosing the blueberry buckle. It's a nice thick cake with two layers of blueberries, and a crumb layer on top. The cake and crumbs are made with whole wheat pastry flour and spelt flour. The cake has great flavor and texture - Kim Boyce's recipes are awesome! We ate some of it for dessert tonight but it is really more of a breakfast cake...mmmm, I can't wait to eat some tomorrow morning =)

Whole grain blueberry buckle
Adapted from Good to the Grain
Serves 8-10

Streusel topping:
1/2 cup whole wheat pastry flour
1/2 cup spelt flour
3 tbs white sugar
1 tbs dark brown sugar
1/2 tsp baking powder
1/2 tsp ground cinnamon
1/4 tsp kosher salt
3 tbs cold unsalted butter, cut into 1/4-inch pieces
1 egg

Cake:
1 1/4 cups spelt flour
1 cup whole wheat pastry flour
1/2 cup dark brown sugar
1/2 cup white sugar
1 tbs baking powder
1 tsp ground cinnamon
1 tsp kosher salt
1 stick (8 tbs) unsalted butter, softened
3/4 cup whole milk
1/3 cup plain yogurt
4 egg yolks
2 tsp vanilla extract
2 cups blueberries

Preheat oven to 350 deg F and butter a 2 1/2-quart baking dish.

To make the streusel topping, sift the flours, sugars, baking powder, cinnamon, and salt into a large bowl. Pour whatever remains in the sifter into the bowl. Add the 1/4-inch pieces of butter to the bowl and use your fingertips to mix them into the dry ingredients. Rub the butter between your fingertips, breaking it up into smaller pieces. Continue until the mixture resembles coarse cornmeal. Whisk the egg well and pour it over the dry ingredients. Using your hands, mix the egg in until the mixture forms clumps.

To make the cake batter, sift the flours, sugars, baking powder, cinnamon, and salt into the bowl of a stand mixer. Pour whatever remains in the sifter into the bowl and add the softened butter to the dry ingredients. Using the paddle attachment on medium speed, mix until the butter is well combined with the flour mixture.

Whisk together the milk, yogurt, egg yolks, and vanilla extract in a medium bowl until well combined. Add the wet mix to the stand mixer bowl and blend on low speed until the mixture forms a smooth batter.

Spread half of the batter in the buttered dish and top with half of the blueberries. Spread the other half of the batter over the blueberry layer and sprinkle the remaining blueberries over the top. Top with the streusel mixture.

Bake the buckle for 60-70 minutes, rotating the pan halfway. The cake is finished when it is golden brown and springs back when touched lightly, or when a toothpick inserted in the center comes out clean. Allow the buckle to cool in the pan. The buckle can be served warm or cool, and can be kept for a couple days if wrapped well with plastic.