1. In medium-size bowl, beat butter, peanut butter, light-brown sugar, 3/4 cup granulated sugar and vanilla in bowl until smooth and creamy, 3 minutes. Beat in eggs.
2. In small bowl, mix flour, cocoa and salt. On low speed, beat into butter mixture. Refrigerate 15 minutes.
3. Heat oven to 375 degrees F. Roll dough into balls, 1 tablespoon each. Roll each ball in the 1/4 cup sugar. Transfer to ungreased baking sheet, spacing 1 inch apart.
4. Bake in 375 degrees F oven until set, 10 minutes. Press an unwrapped chocolate candy in center of each cookie. Return to oven; bake 1 minute to set.
5. Let cool slightly on sheet on rack. Remove cookies to rack; let cool completely. Store cookies in airtight container up to 2 weeks (chocolate centers will firm up overnight).