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.
In small bowl, mix flour, cocoa and salt. On low speed, beat into butter mixture. Refrigerate 15 minutes.
Heat oven to 375°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.
Bake in 375°F oven until set, 10 minutes. Press an unwrapped chocolate candy in center of each cookie. Return to oven; bake 1 minute to set.
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).