Step 1 Cream butter and sugar. Add eggs and mix thoroughly.
Step 2 Sift together flour, cream of tartar and baking soda. Add to butter mixture. Mix well. Add milk and coconut milk.
Step 3Line bottoms of 2 (8-inch) round cake pans with parchment paper and coat with nonstick cooking spray. Divide batter between pans. Bake cakes at 350 degrees until toothpick inserted in center comes out clean, 20 minutes. Cool in pans on rack, then remove.