To make the cake layers: preheat the oven to 350ºF. Grease and line the bottoms of three 8-inch cake pans with parchment paper and set aside.
In a large bowl, sift together the flour and baking powder, then lightly stir in the salt and set aside.
In a stand mixer fitted with a paddle attachment, cream together the butter, coconut oil, and sugar on medium-high speed for 3-4 minutes, until light and fluffy. Add the eggs one at a time, beating well after each addition. Reduce the mixer speed to low and add the vanilla extract and sour cream. Gradually add the dry ingredients and mix until about 80% combined. This prevents overmixing the batter after adding the Food Coloring. Divide the batter evenly into three bowls. Using a kitchen scale ensures accurate division.
In the first bowl, add ¼ cup of milk and the carrot juice. Fold the ingredients together until smooth and just combined. Carrot juice provides a natural, vibrant orange hue.
In the second bowl, add ¼ cup of milk and the beet juice. Fold until smooth. Beet juice offers a beautiful, natural pink to red color, depending on its concentration.
In a blender, combine the mint leaves with the remaining ½ cup of milk and blend until very smooth. Add this mixture to the third bowl and fold until just combined. This creates a naturally green-tinted batter.
To make the buttercream frosting: In a stand mixer with a paddle attachment, beat the butter and cream cheese until creamy. Gradually add the powdered sugar, then mix in the salt, vanilla extract, and heavy cream. Mix until smooth and creamy. While this recipe uses natural colors, you could easily incorporate traditional food coloring into the frosting for bolder, more vibrant shades. Gel food coloring typically provides the most intense color payoff.
To frost the cake: Level the tops of the cake layers. Stack the layers with a layer of frosting between each. Frost the entire cake and decorate as desired. Consider using contrasting colors of frosting to accentuate the naturally colored layers, creating a visually stunning dessert. Piping techniques and edible decorations can further enhance the presentation.
To make a mini cake: Stack the leveled cake scraps, patting them firmly to adhere. Cut out four 2 ½-inch circles using a biscuit cutter. Stack the circles and, if desired, wrap the mini cake tightly in plastic wrap and freeze for easier frosting. Frost the frozen cake and let it come to room temperature before serving. A chilled cake is firmer and easier to frost intricately.
