1. Prepare the Streusel Topping:
* In a medium bowl, whisk together the 1 cup of all-purpose flour, granulated sugar, light brown sugar, ground cinnamon, and salt for the streusel.
* Add the cold, cubed butter to the dry ingredients.
* Using your fingertips, a pastry blender, or a fork, cut the butter into the flour mixture until it resembles coarse crumbs with some larger, pea-sized pieces.
* Place the streusel mixture in the refrigerator to keep it cold while you prepare the cake batter. This helps it stay crumbly during baking.

2. Prepare for Baking:
* Preheat your oven to 350°F (175°C).
* Grease and flour a 9×13 inch baking pan. Alternatively, line the pan with parchment paper, leaving an overhang on two sides to easily lift the cake out later.

3. Combine Dry Ingredients for the Cake:
* In a separate medium bowl, whisk together the 2 ½ cups of all-purpose flour, baking powder, baking soda, and salt for the cake. Set aside.

4. Cream Butter and Sugar:
* In a large mixing bowl, using an electric hand mixer or a stand mixer fitted with the paddle attachment, beat the softened ¾ cup of unsalted butter and 1 ½ cups of granulated sugar together on medium-high speed until light and fluffy. This usually takes about 3-5 minutes. Scrape down the sides of the bowl as needed.

5. Add Eggs and Vanilla:
* Add the eggs one at a time, beating well after each addition until fully incorporated.
* Beat in the vanilla extract.

6. Alternate Dry and Wet Ingredients:
* Reduce the mixer speed to low. Add about one-third of the dry ingredient mixture to the wet ingredients, mixing until just combined.
* Add half of the sour cream (or yogurt), mixing until just combined.
* Repeat with another third of the dry ingredients, then the remaining sour cream, and finally the last third of the dry ingredients. Mix only until the flour is no longer visible. Be careful not to overmix; overmixing can lead to a tough cake.

7. Prepare and Add Blueberries:
* In a small bowl, gently toss the blueberries with the 1 tablespoon of flour. This helps prevent them from sinking to the bottom of the cake.
* Gently fold the flour-coated blueberries into the cake batter using a rubber spatula.

8. Assemble the Cake:
* Pour half of the cake batter into the prepared baking pan and spread it evenly with an offset spatula or the back of a spoon.
* Sprinkle about half of the chilled streusel topping evenly over the batter.
* Carefully spoon or pour the remaining cake batter over the streusel layer, spreading it as evenly as possible. It might be a bit tricky, but do your best to cover the first streusel layer.
* Sprinkle the remaining streusel topping evenly over the top layer of batter.

9. Bake the Coffee Cake:
* Place the baking pan in the preheated oven.
* Bake for 45-55 minutes, or until the top is golden brown and a wooden skewer or toothpick inserted into the center of the cake comes out clean or with a few moist crumbs attached (but no wet batter). Baking time can vary depending on your oven.
* If the top starts to brown too quickly, you can loosely tent the cake with aluminum foil for the remainder of the baking time.

10. Cool and Serve:
* Once baked, remove the coffee cake from the oven and place it on a wire rack to cool in the pan for at least 20-30 minutes before slicing and serving. This allows the cake to set properly.
* If you lined the pan with parchment paper, you can use the overhangs to lift the cake out onto the wire rack to cool completely.
* Slice into squares and enjoy warm or at room temperature.