Preheat oven to 350°F (175°C) and grease an 8-inch square pan.

In a bowl, mix flour, sugar, and butter until crumbly.

Set aside ½ cup of the mixture for the topping.

Add baking powder, salt, egg, milk, and vanilla to the remaining mixture. Stir until smooth.

Pour batter into the pan and sprinkle with reserved crumb mixture and cinnamon.

Bake for 30-35 minutes. Let cool before serving.

Dust with powdered sugar and serve.