Preheat oven to 375°F.
In an electric mixer, beat shortening and peanut butter until combined. Add sugars and mix until fluffy before adding egg, milk and vanilla.
In a separate bowl, stir together flour, baking soda and salt until combined. Gradually add dry mixture to wet mixture; beat to incorporate.
Shape dough into 1-inch balls and roll in remaining sugar. Place on parchment-lined baking sheet.
Bake cookies 8 to 10 minutes or until lightly browned. Remove from oven and quickly press chocolate into the center of each cookie. Remove cookies from baking sheet and cool on wire rack.