In a stand mixer bowl, combine melted butter, brown sugar, granulated sugar, and vanilla. Mix on low until combined. While mixing on low, add the eggs one at a time, followed by the dry ingredients.

Use a rubber spatula to fold in the M&Ms and chocolate chips. Cover the bowl with plastic wrap and chill in the refrigerator for 30 minutes.

Preheat the oven to 350°F and line a cookie sheet with parchment paper. After chilling, use a large cookie scoop (about 2 1/2-3 tablespoons of dough per cookie) to scoop dough onto the cookie sheet, spacing about 2 inches apart.

Bake for 10-12 minutes, or until the edges are just set.

When the cookies come out of the oven, use a round cookie cutter or glass to gently reshape them. Let cool for 4 minutes on the baking sheet before transferring to a cooling rack to cool completely. Place cookies in the freezer for 15 minutes to chill.

Place a chilled cookie top down and scoop vanilla ice cream on top. Gently spread to the edges and place another cookie on top, pressing gently. Roll the sides in mini chocolate chips, M&Ms, or sprinkles.

Wrap each sandwich tightly with plastic wrap and place in the freezer. Repeat until all sandwiches are made. Freeze for at least 3 hours before serving, or up to 3 months!