Blueberry Grunt (Upside Down Cake)

Recipe is from an unknown source. We've just been making it forever.

BAKE AT 350F 45-50 MINS. 9 INCH SQUARE PAN ¼ cup melted butter or marg ½ cup brown sugar 2 cups blueberries (fresh or frozen) 1 tbsp. Lemon juice ½ cup butter ¾ cup granulated sugar 1 egg 1 tsp. Vanilla 1 1/3 cups all purpose flour 2 tsp baking powder ¼ tsp. Salt 1 tsp. Cinnamon ¾ cup milk

In cake pan, melt butter/marg. Then combine with brown sugar; spread evenly on bottom. Then spread blueberries evenly over top, sprinkle with lemon juice. Cream butter/marg gradually add sugar, beat until light. Beat in egg, vanilla and milk. In a separate bowl, sift or mix flour, baking power, salt and cinnamon. Add dry ingredients to creamed mixture; spread batter evenly over blueberries. Bake until center comes out clean. Let cool 10 mins. in pan then turn out onto a plate.