Preheat the oven to 350 F. Line a 12 cup muffin pan with paper liners. In a large bowl, whisk together flour, sugar, salt, and baking powder. Add in milk, vegetable oil, eggs, and vanilla extract, and whisk until smooth.
Evenly divide the cupcake batter between the prepared muffin pan. Bake for 15-18 minutes. Let cool completely before frosting. For the frosting, mix the butter with powdered sugar, vanilla extract, and milk until combined.
Frost the cooked cupcakes. Place pink sanding sugar into a shallow dish. Cut each marshmallow in half, and dip each half into the sanding sugar. Place them on each cupcake to look like bunny ears.