In mixing bowl, cream butter, peanut butter and sugars; add egg and vanilla.
Stir together flour, baking soda and salt; add to creamed mixture. Mix well. Chill for 1 hour.
Preheat oven to 325 F. Shape dough into 48 balls, 1-inch each. Place in lightly greased mini muffin tins. Bake for 14-16 minutes or until lightly browned.
Remove from oven and immediately make “wells” in the center of each by lightly pressing with a melon baller. Cool in pans for 5 minutes, then carefully remove to wire racks.
For filling: melt chocolate chips in double boiler over simmering water. Stir in milk and vanilla; mix well. Using a small pitcher or pastry bag, fill each cooled shell with filling. Sprinkle with peanuts.
Note: I have made these for years at Christmas and my family just loves them.