1/2 cup butter
1 cup blueberries, rinsed and drained
1 teaspoon distilled white vinegar
1 cup white sugar
2 eggs
1 teaspoon vanilla extract
1 quart milk
1 teaspoon vanilla extract
1 teaspoon blueberry extract
Preheat oven to 350 degrees F (175 degrees C). Grease and flour 2 (8 ounce) pans. Stir together the flour, baking powder, baking soda, and salt.
In a large bowl, cream together the butter, blueberries, vinegar, sugar, eggs, and vanilla until smooth. Beat in the flour mixture, then beat in the milk, 1 teaspoon at a time, mixing just until incorporated. Fold in the blueberry extracts and blueberry preserves. Drop by tablespoonfuls into the prepared pans.
Bake in the preheated oven for 60 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool. Wrap aluminum foil and refrigerate.