Lightly grease and flour a 10 inch tube pan. Line the bottom with a circle of waxed paper to fit pan. Grease the waxed paper. Preheat oven to 325 degrees. Sift together flour, baking powder, salt and cocoa. Cream the butter at high speed for 3 minutes. Beat in sugar in 3 additions, beating well after each portion. Beat in eggs one at a time. Continue beating for at least 3 minutes after the last egg addition. Blend in "Adams Best" Vanilla, Adams Butter Flavoring and Adams Chocolate Extract. Reduce speed to low, alternately add sifted dry ingredients in 3 additions with milk in 2 additions. Add sour cream and beat for 4 minutes on low speed. Carefully pour and scrap batter into tube pan. Shake and tap pan gently to level batter. Bake on the lower-third-level rack for 75 to 90 minutes, or until wooden pick inserted in the center comes out clean. Allow to cool in pan for 5 minutes. Carefully invert on cooking rack and remove waxed paper. Allow to cool completely.