Step 1: Preheat your oven to 350°F (175°C) and grease two 8-inch round cake pans.
Step 2: In a large bowl, whisk together the flour, sugar, baking powder, and salt.
Step 3: Add the softened butter and half of the milk. Beat on low speed until combined, then increase to medium for 2 minutes.
Step 4: In a separate bowl, whisk the remaining milk, egg whites, and vanilla extract.
Step 5: Gradually add the egg white mixture to the batter in three parts, beating well after each addition.
Step 6: Divide the batter evenly between the prepared pans and bake for 30-35 minutes or until a toothpick comes out clean.
Step 7: Allow cakes to cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.
Step 8: Divide the buttercream into bowls and tint with gel food coloring. Stack the cakes with a layer of frosting in between.
Step 9: Apply a thin crumb coat of frosting over the entire cake and chill for 20 minutes.
Step 10: Use a grass piping tip to cover the cake with ‘fur’ and place candy eyes and marshmallow teeth to finish your monster.