In a small bowl, add the bittersweet chocolate and butter. Place over a small saucepan of simmering water, and stir often until fully melted. Remove from the double boiler and allow to cool for a few minutes.

Meanwhile, in a large bowl, add the sugars, eggs, and vanilla.

Using an electric mixer, beat on high speed for about 5-6 minutes until the mixture has doubled in size. Scrape down the bowl to make sure everything is properly combined.

While mixing on low speed, slowly pour in the chocolate butter mixture.

Once it is fully combined, add the flour, cocoa powders, and salt, and fold until mostly combined.

Lastly, fold in the M&Ms until evenly dispersed.

Pour the brownie batter into the prepared pan and smooth out the top with an offset spatula. Top with more M&Ms, if desired.

Bake the brownies for about 35 minutes.

Allow them to cool completely in the pan before removing.

Use a heart shaped cookie cutter to cut out as many hearts as you can. Alternatively, use a sharp knife to cut them into 16 squares