Begin by melting ½ cup of butter, 2 ounces of semi-sweet chocolate, 1 cup of brown sugar, and ¾ cup of granulated sugar together in a double boiler over simmering water. Stir gently until the mixture becomes glossy and smooth, which typically takes about 5-7 minutes. Once melted, remove it from heat and allow it to cool for 5-10 minutes until it’s comfortably warm.

Next, add 4 beaten eggs to the cooled chocolate mixture, one at a time. Whisk each egg in thoroughly until the mix is silky smooth and homogeneous. This process should take around 3-5 minutes.

With the egg mixture ready, gently fold in 2/3 cup of cocoa powder, ½ teaspoon of salt, and 1 teaspoon of vanilla extract. Use a spatula to mix until no dry cocoa powder is visible; this should take 1-2 minutes.

Now, sift in ¾ cup of all-purpose flour to the chocolate mixture. Carefully fold the flour in using a spatula until just combined, allowing some streaks of flour to remain visible.

Line an 8 x 8 inch baking pan with parchment paper, ensuring to leave some overhang for easy removal later. Pour the brownie batter into the prepared pan, smoothing the top with a spatula for an even surface.

Generously sprinkle 1 cup of M&M’s over the top of the brownie batter, being careful not to press them in.

Preheat your oven to 350°F (175°C) and place the brownie pan in the center. Bake for 45-50 minutes, checking for doneness after 40 minutes.

After baking, remove the brownies from the oven and let them cool completely in the pan on a wire rack, which should take about 1-2 hours. Once cooled, lift the brownies out using the parchment overhang, and slice them into squares.