Preheat your oven to 350°F (175°C) and prepare two baking sheets with parchment paper.

Cream together 1 cup of softened unsalted butter, 3/4 cup granulated sugar, and 3/4 cup brown sugar in a large bowl until light and fluffy.

Beat in 1 large egg until well combined.

Whisk together 2 1/4 cups all-purpose flour, 1 tsp baking soda, and 1/2 tsp salt in another bowl. Gradually add to the wet ingredients until just combined.

Fold in 1 cup of M&Ms into the dough, saving some for pressing on top.

Scoop tablespoonfuls of dough onto the prepared baking sheets, placing them about two inches apart. Press additional M&Ms on top.

Bake for 10-12 minutes until edges are golden and centers feel soft. Let cool slightly before enjoying.