upside down blackberry cake

1 1/2 c. fresh or frozen blackberries (if using frozen do not thaw)
1 c. butter
1 c. sugar
3 eggs
2 t. lemon juice
1 t. vanilla
2 c. flour
1 1/2 t. baking soda
1/2 t. salt
2/3 c. milk
Line bottom and sides of a 9" square pan with aluminum foil, then spray with nonstick spray. Place 1/2 c. berries in pan.
In a bowl combine butter and sugar. Add in eggs, lemon juice and vanilla. Mix well. Add flour, baking soda, salt and milk. Fold in berries. Spoon batter over berries in pan. Bake at 350 for 45-55 minutes. Cool for 10 minutes. Invert onto serving platter and remove foil. Serve with whipped cream.