Preheat oven to 375 degrees. Grease a 9 x 13-inch baking pan.
Melt chocolate and butter in a saucepan over low heat, set aside.
In the bowl of a stand mixer, beat eggs, sugar, and vanilla, on medium-high speed for 10 minutes. Stop the mixer, and pour in the melted chocolate mixture, flour and salt, blend until just mixed. Stir in the nuts by hand. Pour into prepared pan.
Bake for 35-40 minutes. (Don't over bake.) Cool for 5-10 minutes, then top with 2 cups M&M's, lightly pressing them into the brownies. Makes 24 brownies