Blend sugar, flours, milk powder, baking powder, and salt with a wooden spoon until thoroughly combined. May take awhile to do!
Add butter and vanilla until the mixture resembles coarse meal.
Preheat the oven to 350 degrees. Grease and flour a 9 X 13 cake pan.
Beat the prepared cake mix with a wooden spoon, warm water and room-temperature eggs until the mixture is smooth.
Scrape the batter into the prepared cake pan and bake until a toothpick inserted in the center comes out clean, about 25 minutes for two 9-inch layer cakes, 35 mins for a 9 X 13 cake pan. Cool the cake in pan for 10 minutes, then turn out onto a wire rack.