Use a small spoon to scoop a small hole into the center of each cooled cupcake. Set aside.
In a large bowl, use an electric mixer to beat the butter until smooth and fluffy. Gradually mix in confectioners sugar. Add vanilla and 2 Tablespoons of heavy whipping cream; beat for an additional 3-4 minutes.
Test to see if the frosting can form and hold a stiff peak by taking a spoonful of frosting and turning the spoon upside down. If the frosting stays on the spoon it is ready if not then add more confectioners sugar ½ cup at a time. If too thick, mix in more cream.
Add several drops of green gel food coloring and mix until color is even throughout.
Spoon frosting into a piping bag fitted with a small flower tip. Start by frosting on the outside edge of the cupcake, working in towards the center. Frost around the hole in the center of the cupcake.
Place a peep into the hole so that the top half of its body sticks out of the cupcake. Add a few icing flowers to decorate the cupcakes, if desired.
Notes
Store cupcakes in an airtight container at room temperature for up to 3 days.