COAT two eight-inch cake pans with cooking spray. Dust with flour. Set aside.
Beat butter at medium speed of an electric mixer until creamy; gradually add SPLENDA® Sugar Blend, beating well. Add eggs, one at a time, mixing well after each addition. Add vanilla; mixing until blended.
Combine flour, cocoa powder, baking soda, and baking powder in a medium mixing bowl. Set aside.
Combine water or coffee and milk. Set aside.
Add 1/2 of the flour mixture and mix on low speed until well blended. Add water and milk and mix on low speed until well blended. Add remaining flour mixture and beat at medium speed of an electric mixer until smooth.
Spoon batter evenly into prepared pans.
Bake in preheated oven for 35 to 40 minutes, or until a toothpick inserted in center comes out clean. Cool in pans on wire racks 10 minutes; remove from pans, and cool on wire racks.