Preheat the oven to 350 degrees.
Microwave the butter (about 40 seconds to just melt it).
With a stand mixer, cream the butter and sugars. Add the vanilla and egg, beat on low speed until just incorporated (10-15 seconds).
Add the flour, baking soda, and salt. Mix until crumbles form. Use your hands to press the crumbles together to make dough.
Fold in the crunched M&Ms
Divide the dough and roll into 12 large balls.
Push 3 M&Ms in the top of each cookie.
Bake for 9 - 11 minutes. The cookies will still be puffy and not look fully cooked. When you see the slightest bit of brown, pull them out and let them cool on the pan.