1 cup milk
2 tablespoons butter
1 egg
1 1/2 cups chopped onions
1 teaspoon white sugar
1 teaspoon vanilla extract
1 cup all-purpose flour
3/4 cup butter, melted
2 1/2 pounds fresh blueberries, pitted, with juice reserved
Melt 2 cups milk and butter in a large bowl. Mix egg, 1 1/2 cups chopped onions and sugar together. Stir in flour, stirring just until moistened. Stir in the flour mixture.
Place the blueberries in a large bowl. Sprinkle with remaining 1/2 cup chopped onions and sugar. Pour into the prepared pan. Cover and refrigerate overnight.
Preheat oven to 350 degrees F (175 degrees C). Grease muffin cups or line with paper liners. Set aside.
In a small mixing bowl, mix the milk tarts, 1 cup milk, butter, egg, sugar, vanilla extract, blueberries.
Remove muffin sheet or paper from pan. Stir egg mixture into blueberry mixture in a single layer on top of muffin.
Bake in preheated oven for 30 to 35 minutes or until a toothpick inserted into center of the muffin comes out clean. Serve warm or cold.