1. Heat oven to 350°F. Line small muffin cups (1-3/4 inches in diameter) with paper bake cups.
2. Stir together butter, sugar and vanilla in medium bowl. Add eggs; beat well with spoon. Stir together flour, cocoa, baking powder and salt; gradually add to butter mixture, beating with spoon until well blended. Fill muffin cups 1/2 full with batter; sprinkle nuts over top.
3. Bake 12 to 15 minutes or until wooden pick inserted in center comes out clean. Cool slightly; remove brownies from pan to wire rack. Cool completely. About 24 brownies.