My all-time favorite best brownie recipe made in a loaf pan has been oh-so-perfected over the years. As if cutting the brownies in half into two giant bakery-sized pieces isn't fun enough, I then stirred in pretty M&Ms, but other fun things to stir in or press into the surface include mini chocolate chips, your favorite chopped chocolate bar, chopped pieces of crystallized ginger (oh yes), chopped candy bars (especially the ones with caramel!) and even sprinkles!
Preheat the oven to 325 degrees F. Line a 9-by-5 inch loaf pan with parchment paper.
Melt the butter in a small saucepan over low heat. Add the sugar and cocoa powder and cook, stirring often, until the mixture is melted and smooth, about 3 to 4 minutes. Transfer to a medium bowl and let cool slightly. (Alternatively, combine the butter, sugar and cocoa powder in a microwave-safe bowl and microwave on high for 30 seconds. Stir, then microwave on high for another 30 seconds.)
Stir in the salt and vanilla, then let the mixture cool for 1 minute more. Add the egg and stir until incorporated. Add the flour and stir for 50 brisk strokes.
Spread the batter into the prepared pan and sprinkle the candy-coated chocolate candies on top. Bake until a toothpick inserted in the center comes out with fudge crumbs clinging to it and the surface is shiny and starting to crack, about 23 minutes.
Let cool completely in the pan, then lift out using the parchment paper. Slice in half or into four pieces and serve.