Set your oven to 350°F (175°C) and prepare a muffin pan by lining it with cupcake liners.
In a mixing bowl, whisk together the flour, baking powder, and salt until well combined. Set aside.
Cream butter and sugar until light and fluffy. Beat in eggs one at a time, followed by vanilla extract.
Add dry ingredients alternately with milk, mixing until smooth.
Spoon the batter evenly into the cupcake liners and bake for 18–20 minutes, or until a toothpick inserted in the center comes out clean. Cool completely.
Tint the buttercream with blue gel food coloring until you achieve a vibrant Cookie Monster blue.
Pipe frosting using a star tip to create a furry texture.
Insert half an Oreo or a mini cookie into the frosting to form the mouth. Add two edible eyes to finish the look.
