Preheat the oven to 350°F (175°C). Grease and line three 9-inch cake pans.
Prepare the base batter: Cream the butter and sugar until light and fluffy. Add eggs one at a time, followed by vanilla and milk.
Divide the batter evenly into three bowls.
Flavor each layer: Mix cocoa and milk into one for chocolate. Leave one plain for vanilla. Add strawberry puree to the third for the strawberry layer.
Bake for 25–30 minutes or until a toothpick inserted in the center comes out clean.
Cool completely on wire racks before assembling.
Frost and decorate: Stack in chocolate-vanilla-strawberry order, spreading buttercream between each layer and around the outside.
