Preheat your oven to 375°F (190°C). Line two baking sheets with parchment paper or silicone baking mats. Set aside.

In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.

In a large mixing bowl, using an electric stand mixer fitted with the paddle attachment (or a hand mixer), cream together the softened butter, granulated sugar, and light brown sugar on medium speed until light and fluffy, about 2-3 minutes.

Beat in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract until just combined.

Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix; stop as soon as no dry streaks of flour remain.

Fold in 1 1/2 cups of M&M's candies using a rubber spatula until evenly distributed throughout the dough.

Drop rounded tablespoons of cookie dough (or use a 1.5-inch cookie scoop) onto the prepared baking sheets, spacing them about 2 inches apart. If desired, press a few extra M&M's onto the top of each cookie dough ball for a prettier finish.

Bake for 10-12 minutes, or until the edges are golden brown and the centers are just set. Do not overbake; the cookies will continue to set as they cool.

Remove the baking sheets from the oven and let the cookies cool on the sheets for 5 minutes before transferring them to a wire cooling rack to cool completely.