In an 8 inch square baking dish, mix blueberries, 3 tablespoons sugar, and orange juice. Set aside. In a small bowl, thoroughly mix flour, baking powder, and salt. Set aside.
In a medium bowl, cream butter and 1/2 cup sugar until light and fluffy. Beat in egg and vanilla extract. Gradually add flour mixture, stirring just until ingredients are combined. Drop batter by rounded tablespoons over blueberry mixture. Try to cover as much of filling as possible.
Bake in preheated oven for 35 to 40 minutes, until topping is golden brown and filling is bubbling.
