Begin by preheating the oven to 350°F / 175°C and line a muffin pan.

Whisk 1 1/4 cups all-purpose flour, 1 cup sugar, 1 1/2 tsp baking powder, and 1/2 tsp salt together in a large bowl.

Make a well in the middle of the dry ingredients and add 1/2 cup of buttermilk, 1/2 cup water, 1/4 cup vegetable oil, 1 large egg, and 1 Tbsp vanilla extract into the opening. Whisk the wet ingredients together, then whisk them into the dry ingredients. Mix until the batter is smooth. If you want to add sprinkles, fold 1/4 cup of rainbow sprinkles into the batter.

Divide the batter evenly between the cupcake liners, filling them about 3/4 of the way full. Bake for 18-20 minutes or until a toothpick comes out clean.

Let the cupcakes cool for 10 minutes before moving them to a cooling rack to finish cooling. If you want to accelerate the cooling process, pop the pan into the freezer for about 30 minutes.

Beat 2 cups of unsalted butter on a medium speed for 30 seconds until smooth with a paddle attachment / stand mixer or a hand mixer.

Mix in 1 Tbsp vanilla extract or vanilla bean paste and 1/2 tsp salt on a low speed.

Slowly add in 7 cups of powdered sugar while mixing slowly on the lowest setting. Halfway through add in 3 Tbsp of heavy cream or milk to make it easier to mix. I like to place a kitchen towel over my mixer to contain any powdered sugar clouds.

Mix on low until the ingredients are fully incorporated and the desired consistency is reached. Scrape the sides and bottom of the bowl as needed with a rubber spatula.

If the frosting seems too thick, add additional cream (1 Tbsp at a time). If the frosting is too thin, add more powdered sugar (a quarter of a cup at a time).

Divide frosting evenly between six bowls and color with gel food coloring. Leave one bowl of frosting uncolored to fill and crumb coat the little monster cakes. I colored the remaining bowls purple, orange, blue, green, and pink.

Place the colorful frosting into piping bags fitted with your favorite frosting tips. I used a small grass tip and a small French piping tip to make the monsters look furry.

Unwrap two cupcakes. Spread a dab of frosting onto a small, greaseproof cake board. This will help keep the cupcake stack in place on the board.

Place one cupcake in the center of the board. Spread an even layer of frosting on top of the cupcake, then top it with the second cupcake.

Insert a wooden skewer through the center of the cupcakes, then carefully cover the cupcake stack in a thin layer of frosting.

Freeze the stacked cupcakes for 5-10 minutes, until the frosting is firm to the touch.

Remove the cupcake stack from the freezer and pipe on a second layer of frosting with colorful frosting.

Add on sprinkle or fondant eyes and fondant facial features of your choice. Repeat with the remaining cupcakes, creating different colored monsters with a variety of expressions. You can also stack up to 3 cupcakes to make a taller monster, or avoid stacking all together and make shorter monsters using 1 cupcake.