Preheat oven to 350°F. Grease 10-inch angel food tube pan or an extra deep 9x13 baking dish.
Filling ingredients: In a large bowl, mix together the 1/2 cup brown sugar, 1/2 cups chopped pecans, and 1 1/2 teaspoons ground cinnamon. Keep the blueberries separate. Set aside.
Topping ingredients: In a separate bowl, make the topping by whisking together the 1 cup granulated sugar, 1/4 teaspoon salt, 1 cup all-purpose flour, and 1 tablespoon ground cinnamon. Add the melted 6 tablespoons butter, stirring until well combined. Set aside.
Mix the cake ingredients: To make the cake, sift together the 2 1/2 cups all-purpose flour, 1 1/2 teaspoons baking powder, 1 1/2 teaspoon baking soda, and 1/2 teaspoon salt. Set aside. In the bowl of your stand mixer, cream together 3/4 cup unsalted butter and 1 1/4 cup granulated sugar using the paddle attachment on high speed until light and fluffy. Stir in 3 eggs and 2 teaspoon vanilla extract on low speed until combined. Beat in the flour mixture alternately with the 1 1/2 cups sour cream, scraping sides as needed. Do not over mix.
Prepare the coffee cake: Spread 1/3 of the cake batter in the prepared pan. Cover with 1/2 of the filling mixture. Then top with half of the 3 cups fresh blueberries. Add another third of the cake batter and gently spread. Add the remaining filling ingredients, and then top with the remaining blueberries. Add the remaining cake batter. Use a spatula to gently spread.Sprinkle the streusel topping mixture over the batter in the pan.
Bake the coffee cake: Bake in the preheated oven for 55-65 minutes, or until a toothpick inserted into the center of the cake comes out clean. You can also verify that the internal temperature is about 200°F to verify that it is done in the middle. Remove the cake from the oven and allow it to cool in the pan for about 10 minutes.
Notes
Best if served the same or very next day. Store in an airtight container.Serving: If using an angel food tube pan, lift the bottom out of the pan (remove sides) to allow cake to finish cooling. Once completely cool, you can loosen the cake from the center and bottom with a knife and then use a couple spatulas to lift the cake off of the cake pan bottom and transfer to a platter.