Mix together the fruity pebbles and buttermilk for the cereal milk fruity pebble cake batter.
Cream the butter, oil, and sugar, then add the eggs, extracts, buttermilk and dry ingredients and mix to combine.
While the cakes are baking, combine the cake crumb ingredients and bake at 300 F for 15 minutes.
Frost the cake layers with an even layer of the cereal milk buttercream.
Sprinkle the top of the buttercream with the the fruity pebble cake crumbs. Then frost the entire cake with the rest of the buttercream.