Cream together butter, peanut butter, white and brown sugars.
Mix in egg and 1/2 teaspoon of vanilla.
Stir the flour mixture into the creamed mixture.
Shape the dough into 48 balls, 1 inch each. place each ball into one compartment of a mini muffin tin.
Bake for 14-16 minutes or until lightly browned.
Remove from oven and immediately make wells in the center of each using a melon baller (I used an oven thermometer).
Cool in pan for 5 minutes then carefully remove to wire racks.
For the filling
Place chocolate chips in a double boiler over simmering water stir in milk and vanilla and mix well until chips are melted. You can use the microwave if you prefer, cook in 30 second increments until melted.