Preheat your oven to 350°F and grease an 8-inch square baking dish. In a medium bowl, whisk together the flour, baking powder, and salt. In a separate bowl, cream the butter and sugar until light and fluffy. Beat in the egg and vanilla extract.

Gradually add the flour mixture to the butter mixture, alternating with milk. Gently fold in the blueberries, ensuring they are evenly distributed. Pour the batter into the prepared baking dish and spread it evenly.

In a small bowl, mix flour, sugar, and cinnamon. Cut in the butter using a fork or fingers until a crumbly mixture forms. Sprinkle the topping evenly over the batter.

Place the dish in the oven and bake for 40-45 minutes, or until a toothpick inserted into the center comes out clean. Let it cool slightly before serving.

Slice the buckle into squares and serve warm or at room temperature. This treat pairs wonderfully with a scoop of Pineapple Ice Cream for a refreshing twist!