Preheat your oven to 350 degrees F. Coat the cups of a muffin tin with non-stick spray and set aside.
Separate the cookie dough pieces and put 1 piece into each muffin tin cup. Bake for 10-14 minutes (according to the package driections) until the cookies are lightly browned around the edges. (You can work in batches if needed.)
Remove the pan from the oven and immediately use a tart shaper or the bottom of a measuring spoon to gently tap down the center of each cookie to make a little indent/cup.
Let the cookies cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.
Once the cookies are cooled, make the frosting by beating the butter in a large mixing bowl on medium speed until pale, about 2 minutes.
Add the powdered sugar to the butter, one cup at a time, mixing after each addition. Then add the vanilla, salt, and 1 tablespoon of milk and mix to combine. Beat the frosting for 2-3 minutes until light and fluffy. If needed add another tablespoon of milk to thin it out a bit.
Mix in a couple of drops of green food coloring. Add 1-2 more drops as needed to reach your desired color. Transfer the buttercream frosting to a piping bag with a star tip or grass tip in place.
Pipe the frosting into the cookie cups and then top each cup with 3 chocolate eggs.
Notes
Unfrosted cookies can be kept at room temp for up to 1 week in an airtight container. The cookie cups can be frozen for up to 3 months and then thawed overnight in the fridge before decorating.
Frosted cookies can be kept at room temp for up to 3 days in an airtight container.
If you don't have a piping bag and tips, you can add dollops of frosting into each cup with a spoon or cut the corner of a Ziploc bag and use that to pipe the frosting.
You can use homemade sugar cookie dough instead of the prepared stuff. Use 4 teaspoons of cookie dough per muffin tin cup and proceed as directed.