Preheat the oven to 350°F (175°C).

In a mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until smooth.

Beat in the eggs one at a time, then stir in the vanilla extract.

In another bowl, whisk together the flour, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients until well combined.

Fold in the M&M's and chopped nuts (if using).

Drop spoonfuls of dough onto a baking sheet lined with parchment paper, spacing them about 2 inches apart.

Sprinkle additional M&M's on top of each cookie.

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

Allow cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.