Preparation Steps

• Preheat oven to 350°F (175°C). Line a 9-by-9-inch baking pan with aluminum foil and spray with cooking spray; set aside.
• In a large, microwave-safe bowl, melt the butter on high power for about 90 seconds.
• Add the eggs, granulated sugar, light brown sugar, coffee (or water), and vanilla extract to the melted butter. Whisk to combine.
• Add the cocoa powder and instant espresso granules to the wet ingredients. Whisk until incorporated, smooth, and free from lumps. This may take a few minutes if your cocoa powder is lumpy.
• Add the all-purpose flour and stir until it's just incorporated. Do not overmix.
• Turn the batter out into the prepared pan, smoothing the top lightly with a spatula. Bake for 25 to 29 minutes, or until the top has just set, isn't jiggly in the center, and a toothpick inserted into the center comes out clean or with a few fudgy, moist crumbs (but no wet batter).
• Allow the brownies to cool completely in the pan.
• While the brownies cool, prepare the ganache. Add the semi-sweet chocolate chips to a medium, microwave-safe bowl and heat on high power for 1 minute to soften the chips. They will not be fully melted at this point; this is okay. Do not stir.
• Heat the half-and-half or cream in a glass measuring cup or microwave-safe bowl until it begins to bubble and shows signs of just beginning to boil, about 1 minute on high power.
• Pour the hot cream over the softened chocolate chips and let stand for 5 to 10 minutes.
• With a whisk, beat the chocolate and cream mixture until it is silky, smooth, and combined. If the mixture isn't smoothing out, heat it in 15-second bursts in the microwave until it can be stirred smooth.
• Pour the ganache over the mostly cooled brownies (about 30 minutes of cooling is fine; they don't need to be completely cool). Smooth the ganache lightly with a spatula or offset knife.
• Evenly sprinkle the M&Ms over the ganache.
• Cover the pan with a sheet of foil to prevent fridge smells, and place the pan in the refrigerator until the ganache has set up, at least 2 hours. Do not slice the brownies until the ganache has set. These can be made in advance and stored in the fridge; they get better with time.