1. Preheat oven to 350°F. Combine flour, sugar, cocoa, baking powder and salt in large mixing bowl. Add milk, oil and vanilla; mix until blended and smooth.
2. Spoon batter into ungreased 8- x 8-inch glass baking dish. Place cocoa mix in medium bowl. Add boiling water; mix well. Pour evenly over batter. Bake 30 minutes or until wooden pick inserted near center comes out clean.
3. Cool cake 10 minutes. Serve warm with Reddi-wip.