Preheat oven to 350°F.

Place butter in an 8x8 casserole dish and let it melt in the oven while preheating.

In a bowl, whisk together flour, sugar, and milk until smooth.

Remove dish from oven. Pour batter evenly over melted butter—do not stir.

Spoon pie filling evenly over the batter.

Bake for 30 minutes or until the crust is golden brown.

Cool slightly before serving. Best served warm with ice cream or on its own.