Preheat your oven to 350°F and line two standard muffin tins with cupcake liners. Set them aside while you pull together the batter. In the bowl of a stand mixer, add the sugar, flour, cocoa powder, baking powder, baking soda, and salt. Whisk them together until well combined.

Add in the vanilla, eggs, milk, and oil, then mix on low speed, scraping down the sides of the bowl frequently to make sure everything gets incorporated evenly.

Using a measuring cup or cookie scoop, divide the batter evenly between the prepared cupcake liners. Bake for 14–16 minutes or until the centers are set and a toothpick inserted in the middle comes out clean. Let the cupcakes cool completely before you touch the frosting — this step matters, so don't rush it.

To make the frosting, combine the softened butter with about half of the powdered sugar in a clean stand mixer bowl. Mix on low until combined, then add the remaining powdered sugar, salt, vanilla, and milk. Continue mixing until smooth.

Add your green food coloring a little at a time, mixing and checking the color until you get the grass-green shade you want.

Transfer the frosting into a piping bag fitted with a large star tip. Pipe a generous mound of frosting onto each cooled cupcake, then immediately press on the Easter sprinkles and nestle a Peeps marshmallow into the center. The frosting needs to be fresh and slightly soft so the Peeps stick in place.