Beat butter and peanut butter at medium speed with an electric mixer until creamy; gradually add sugars, beating well. Add egg and vanilla, mixing well. Combine flour, baking soda, and salt; add to butter mixture, mixing well. Cover and refrigerate 1 hour.
After 1 hour, remove from refrigerator and roll dough into 48 (1”) balls. Place in lightly greased miniature (1-3/4”) muffin pans and using your thumb make an indentation in the dough (this holds the fudge!).
Bake at 325 degrees for 12-14 minutes or until lightly browned. Cool in pans on wire racks for 5 minutes. Carefully remove the cookies to wire racks to cool completely. (I used a small offset spatula to help tease the cookie out of the tin and it worked great as long as I allowed a few minutes to cool down before removing.)
Spoon warm fudge filling into a heavy-duty, zip-top plastic bag; squeeze bag, piping a small amount of filling into center of each cookie. Sprinkle cookies with chopped peanuts. Cool. Filled cookies may be frozen up to 8 months. Yield: 4 dozen.
2Directions for making fudge filling:
Combine chocolate morsels, condensed milk and vanilla in a heavy saucepan; cook over low heat, stirring often, until morsels melt. Yield 2 cups.
NOTE: Remaining fudge filling can be reheated over low heat and served with pound cake. Or stored in a jar in the refrigerator for a cook’s snack!!!
Cookie is very fragile just out of the oven. I left in oven an additional 2-3 minutes until lightly browned. Left in pan until almost cool. I had a very small baby spoon to fill with fudge. Serve to your favorite people and enjoy! Pat