Preheat your oven to 350F. Line an 8 inch square metal pan with parchment paper and set aside.
Add the chopped chocolate and butter to a large microwave safe bowl.
8 ounces bittersweet baking chocolate, 1 cup salted butter
Microwave in 30 second increments stirring well each time then set aside to cool.
In the large bowl of a stand mixer with the paddle attachment fitted add the sugar and eggs. With the mixer on a medium speed beat for around 5 minutes or until the mixture is pale yellow and has increased in volume.
1 ¾ cups light brown sugar, 3 large eggs
To the mixing bowl, add the cooled chocolate and butter mixture along with the vanilla extract. Turn the mixer to its lowest speed and beat for a minute or until uniform in color. Use a spatula to scrape the bottom of the bowl.
2 teaspoons vanilla extract
Add the flour, cocoa powder, and salt into the mixing bowl. Use a spatula or wooden spoon to gently fold the ingredients together. Stop mixing when there are still a few streaks of flour remaining.
¾ cup sifted all purpose flour, ½ cup cocoa powder, ¼ teaspoon salt
Add the 3/4 cup M&Ms 1/4 cup mini M&Ms and very gently fold them to incorporate into the brownie mixture.
¾ cup M&Ms, ¼ cup mini M&Ms
Transfer the brownie batter to the prepared baking pan, and smooth the top into an even layer.
Scatter the remaining 1/2 cup M&Ms over the top and lightly press them into the brownie batter.
½ cup M&Ms
Bake in the center of the preheated oven for 30 minutes, or until a toothpick inserted into the middle of the brownies comes out with a few fudgy crumbs on it.
Remove from the oven and let it completely cool in the pan before turning out and slicing into squares. Serve and enjoy!
Notes
Bittersweet chocolate: If you're using a sweeter chocolate, like semisweet, slightly reduce the sugar in the brownies. Also, if you can't find bittersweet baking chocolate, a good quality bittersweet chocolate chip will work.
Butter: If you're using unsalted butter, increase the salt by about 1/4 teaspoon.
Cocoa powder: I use regular unsweetened cocoa powder in this recipe.
M&Ms: You can use all mini or all regular sized M&Ms if you prefer.