Line two sheet pans with parchment paper and set aside.

Heat the butter in the microwave or in a saucepan until melted. Once melted, set aside to cool slightly.

In the bowl of a stand mixer, add both the brown sugar and the white sugar.

Feel the melted butter to make sure it isn't too hot. The butter should be warm, still liquid, but not too hot to touch with a finger. Pour the melted butter over the sugars and mix on low until the ingredients are combined and glossy, about 30-45 seconds.

Add in the egg and vanilla and mix on low until the egg is just incorporated.

To the mixing bowl, pour in the flour, baking soda, and salt. Set the mixer to low speed and mix the ingredients until just combined, streaks of flour are ok.

Remove the mixing bowl from the mixer and pour in 3/4 cup of the Valentine M&Ms., Finish mixing the dough by hand using a rubber spatula or a spoon. Gently mix until the M&Ms are evenly distributed and no streaks of flour remain.

Scoop mounds of cookie dough (about two tablespoons in size) and place them on the prepared sheet pans. Space the dough balls about 2 inches apart. If desired, gently press 3-4 M&Ms onto the top of each dough ball for decoration.

Allow the cookie dough to sit at room temperature on the cookie sheets for about 20-30 minutes to let the flour hydrate and absorb the flavors.

While you wait, preheat the oven to 375º.

After resting, the dough will no longer feel sticky, and the cookie dough balls will now be easy to pick up.

Bake the cookies at 375º for 8-10 minutes. The cookies are done when the edges are just starting to lightly brown and the centers have puffed. They will be a little underbaked when you remove them from the oven, but that's what you want. They'll finish setting as they cool.

Allow the cookies to sit for about 10-15 minutes on the sheet pan before transferring them to a cooling rack or a serving platter. The centers will be warm and gooey and the edges will be delightfully crisp and brown.