1. Heat oven to 350°F. Line 2-1/2-inch muffin cups with paper or foil bake cups.
2. Place butter in large microwave-safe bowl. Microwave at MEDIUM (50%) 1-1/2 minutes or until melted. Add cocoa; stir until smooth. Add brown sugar and granulated sugar; stir until well blended. Add eggs and vanilla; beat well. Add flour and 1 cup pecans; stir until well blended. Fill prepared muffin cups about 3/4 full with batter; sprinkle 1 teaspoon remaining nuts over top of each.
3. Bake 20 to 25 minutes or until tops begin to dry and crack. Cool completely in cups on wire rack. About 18 cupcakes.