Preheat oven to 350 degree F. Line a 9x9x2-inch baking pan with foil; grease foil. In a small saucepan melt 1/4 cup butter over medium heat. Stir in brown sugar. Cook and stir until sugar is dissolved. Stir in corn syrup and cream. Bring just to boiling. Stir in nuts. Spread in pan.
Combine flour, cocoa powder, baking powder, baking soda, and 1/2 teaspoon salt; set aside. In a large mixing bowl beat 1/3 cup butter with electric mixer on medium to high speed for 30 seconds. Gradually add granulated sugar, beating on medium speed until well combined, scraping sides of bowl. Add eggs, 1 at a time, beating after each (about 1 minute total). Beat in vanilla. Alternately add flour mixture and milk to butter mixture, beating on low speed after each addition just until combined. Pour into pan, being careful not to disturb nuts.
Bake for 45 to 50 minutes or until a wooden toothpick inserted near center comes out clean. Cool in pan on wire rack 10 minutes. Remove from pan. Carefully peel off foil. Place nut side up on plate. Serve at room temperature.