Blueberry Streusel Coffee Cake

I LOOOOVE coffee cakes, and i love blueberries. After every summer season, i have a freezer packed with frozen blueberries that i failed to use up when they were fresh - which is why recipes like this are perfect! I know it seems like i used a lot of liquid in this recipe, but i made it the first time without the additional 1/3 cup of yogurt and it was super dry, like so dry that it took you a while to swallow. ick. grrrr. Dry + coffee cake = unhappy Gigi. No worries, the extra liquid does the trick.
Now, go blueberry shopping, buy too many, freeze a bunch and make this cake!!!

Streusel -
1/2 cup flour
1/4 cup brown sugar
1/2 t cinnamon
1/2 stick cold unsalted butter, cut into pieces
1/3 cup chopped pecans

Batter -
5 T unsalted butter at room temperature
3/4 cup granulated sugar
2 large eggs
1/2 cup milk
1/2 t pure vanilla extract
1/3 cup plain yogurt or buttermilk
1 3/4 cup flour
2 t baking powder
1/2 t baking soda
1/4 t salt
1 1/2 cups frozen blueberries

Directions:

Preheat oven to 350ºF and grease a 9-inch spring form pan.

To prepare streusel: In a medium bowl, mix together flour, brown sugar and cinnamon. Cut in butter with your pastry blender or fingers until mixture resembles coarse crumbs. Stir in walnuts. Set aside.

To prepare batter: Cream the sugar and butter together, then add the eggs, vanilla, buttermilk or yogurt and milk, afterward, slowly add the dry ingredients until everything is included (except blueberries) in a large bowl with an electric mixer at medium speed. Pour batter into prepared pan and scatter blueberries over the top.

Sprinkle streusel mixture evenly over blueberries. Bake for 1 hour (check at 50 minutes), or until a toothpick inserted in the center comes out clean. Cool cake for 15 minutes in pan on wire rack. Remove side of pan and cool for another hour before serving.