Begin by melting the unsweetened chocolate and butter together using a double boiler or microwave until smooth. Allow it to cool slightly before using.
In a large mixing bowl, combine the sugar and eggs. Use a whisk or electric mixer to beat them together until light and fluffy.
Stir in the vanilla extract into the cooled chocolate and butter mixture, then gradually add it to the sugar and egg mixture, stirring until well combined.
Gently fold in the all-purpose flour until just combined, being careful not to overmix.
Fold in 1 1/2 cups of M&M's into the dough.
Cover the mixing bowl and refrigerate the dough for at least 30 minutes.
Preheat your oven to 350°F (175°C) and line your baking sheet with parchment paper.
Drop rounded tablespoons of dough onto the prepared baking sheet, leaving space between cookies. Press extra M&M's on top for garnish. Bake for 10-12 minutes.
Allow the cookies to cool on the baking sheet for about 5 minutes before transferring them to a wire rack to cool completely.
