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

In a large bowl, cream together softened butter, granulated sugar, and brown sugar until light and fluffy.

Beat in the egg until well combined.

In another bowl, whisk together flour, baking soda, and salt. Gradually add this dry mixture to the wet ingredients until just combined.

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

Scoop tablespoonfuls of dough onto prepared baking sheets about two inches apart. Press extra M&Ms on top.

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