In mixer- combine butter & sugar. Beat on medium speed until light & fluffy.
Turn the mixer to low & add egg & vanilla. Beat until just combined.
Slowly beat in flour & cocoa.
Transfer dough to large piece of parchment paper.
Place another piece on top & roll out to about 1/4 inch thick piece of cookie dough between the 2 sheets of parchment.
Place on cutting board & refrigerate at least 30 minutes.
Once dough is finished chilling- preheat oven to 350 degrees.
Remove top layer of parchment & use your cutters to cut your hearts.
Use a thin spatula to transfer cut out cookies to ungreased cookie sheet.
Place your M&M's on your cookies & bake 10-13 minutes.
Allow to cool on baking sheet completely before transferring to airtight container.
Repeat rolling, cutting & baking until you have used all the dough.