Preheat Oven: Preheat your oven to 350°F (175°C). Grease a 9-inch square baking pan or line it with parchment paper.

Cream Butter and Sugar:

In a large mixing bowl, cream together the softened butter and 1 cup of granulated sugar until light and fluffy.

Add Egg and Vanilla:

Beat in the egg and vanilla extract until well combined.

Prepare Dry Ingredients:

In a separate bowl, whisk together 1 3/4 cups of all-purpose flour, baking powder, and salt.

Alternate Adding Dry Ingredients and Buttermilk:

Gradually add the dry ingredients to the butter mixture, alternating with the buttermilk. Start and end with the dry ingredients. Mix until just combined.

Coat Blueberries:

Toss the blueberries with the remaining 1/4 cup of flour to coat. Gently fold the blueberries into the batter.

Spread Batter:

Spread the batter evenly into the prepared baking pan. Sprinkle the top with 1 tablespoon of granulated sugar.

Bake:

Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center comes out clean. The top should be lightly golden.

Cool and Serve:

Allow the cake to cool in the pan on a wire rack. Serve warm or at room temperature.