Lightly spray a square 8x8-inch baking dish with cooking spray and preheat the oven to 375 degrees F.
In a medium bowl, combine the 2 cups all-purpose flour, 2 teaspoons baking powder, 1 teaspoon ground cinnamon, and 1/4 teaspoon salt. Set aside.
In a separate bowl with a whisk or a mixer, combine together the 1/2 cup butter, 3/4 cup granulated sugar, 1 egg, and 1/2 cup milk until smooth. Slowly add in the flour mixture a little at a time until combined. The batter will be thick.
If using a mixer, turn it off and carefully fold in the blueberries and chopped pecans by hand with a spatula or wooden spoon. Spread evenly in the prepared baking dish. Set aside.
For the streusel topping, in a small bowl combine 1/2 cup granulated sugar and 1/3 cup all-purpose flour together.
Cut in the cubed 1/4 cup cold butter until it resembles a clumpy coarse meal. Evenly spread over the cake mixture in the baking dish.
Place into the oven and bake for 35 to 40 minutes or until a toothpick inserted near the center comes out clean with little to no crumbs. Carefully remove the pan from the oven and allow it to cool completely on a wire rack before cutting to serve.
May leave the cake in the baking dish or cut to store in an airtight container. Store the coffee cake at room temperature up to 3 days.