Preheat oven to 350°F (177°C). Line two large baking sheets with parchment paper or silicone baking mats. (Always recommended for cookies.) Set aside.

Whisk the flour, baking soda, and salt together until combined. Set aside.

In a large bowl using a handheld or stand mixer fitted with a paddle attachment, beat the butter, granulated sugar, and the brown sugar together on high speed until completely smooth and creamy, about 2 minutes. Add the egg and vanilla extract and beat on high speed until combined, about 1 minute. Scrape down the sides and bottom of the bowl as needed to combine. Add the dry ingredients to the wet ingredients and mix on low until combined. Beat in the M&Ms.

Roll cookie dough into very tiny balls, about 1 teaspoon of dough per cookie and arrange on the baking sheets.

Bake for 7-8 minutes or until the edges are lightly browned. Slightly flatten each cookie with the back of a spoon if they didn’t spread much. While the cookies are still warm, I like to press a couple extra M&Ms into the tops. This is just for looks! Allow cookies to cool on the baking sheets for 5 minutes before transferring to a wire rack to cool completely.

Cookies will stay fresh covered at room temperature for 1 week.