Begin by placing a heatproof bowl over a saucepan filled with simmering water to create a double boiler. Combine semi-sweet chocolate, unsalted butter, granulated sugar, and brown sugar in the bowl. Stir occasionally until everything melts into a glossy mixture, which should take about 5-7 minutes. Once melted, remove the bowl from heat and let it cool for 5-10 minutes until it's just warm to the touch.

Once the chocolate mixture has cooled, it’s time to whisk in the eggs. Add them one at a time, using a whisk or spatula to mix until the batter is smooth and shiny; this should take about 1-2 minutes per egg.

Next, add the cocoa powder, vanilla extract, and salt to the batter. Use your spatula or whisk to mix until no dry cocoa streaks remain.

Gently fold in the flour using a spatula, being careful not to overmix. Combine until you see just a few flour streaks remaining.

Line an 8x8-inch baking pan with parchment paper, allowing the edges to hang over for easy removal later. Pour the brownie batter into the pan, smoothing the top with a spatula.

Before baking, sprinkle a generous handful of M&M’s candies over the top of the brownie batter. Press them in gently without submerging them.

Preheat your oven to 350°F (175°C) and bake the brownies for 45-50 minutes. Keep an eye on them—the edges should be firm while the center remains slightly gooey.

Once baked, remove the brownies from the oven and let them cool completely in the pan on a wire rack. This cooling process takes about an hour.