Preheat oven to 350°F (175°C) and butter a 9-inch square pan. For the crumb topping, stir together 1/2 cup flour, brown sugar, cinnamon, and a pinch of salt. Cut in the cold butter until crumbly. Set aside.

Beat the softened butter and granulated sugar until light and fluffy. Add the egg and vanilla, then mix in the yogurt until combined.

Whisk the remaining 1 1/2 cups flour, baking powder, baking soda, and salt in a separate bowl. Stir the dry mixture into the wet mixture just until blended.

Spread half the batter in the pan. Scatter blueberries on top, then dollop the rest of the batter over them and spread gently. Sprinkle the crumb topping evenly over the batter.

Bake for 40 to 45 minutes until a toothpick inserted in the center comes out clean and the topping is golden. Cool in the pan on a wire rack for at least 15 minutes.

Slice into squares and dust with powdered sugar if you like. Serve warm or at room temperature.