Whip the eggs and sugar in the bowl of an electric stand mixer, using the paddle mixer attachment, for 10 minutes. The mixture should be light and fluffy.
While the eggs/sugar are mixing, melt chocolate and butter together over a double boiler set aside to cool.
Add the melted chocolate and vanilla extract to the mixer bowl and mix on medium speed to combine.
Remove mixer bowl and use a wooden spoon to stir in the flour, nuts, and M&M's by hand, just until the flour is combined. Don't over mix.
Using a #24 scoop (3 Tablespoons), drop the cookie dough onto cookie sheets lined with parchment paper or a silicone baking mat. Space dough at least 2 inches apart, as cookies will spread during baking.
Bake for 15-18 minutes, rotating the pans after 10 minutes.
Notes
These cookies are SINFULLY rich and decadent... as evidenced by the calorie and fat content! Feel free to share with a friend...or not!
Recipe adapted from Chef Jenn Malovitz-Solloway at Fox Valley Technical College; Appleton, Wisconsin