Preheat oven to 325 degrees F. Spray a 12-cup standard muffin tin with nonstick cooking spray.: You will feel the kitchen warm as the oven reaches temperature and smell the faint, dry heat; setting the oven correctly is important because it controls how the brownie crumb sets and how the edges bake. If the oven is cooler than intended, the centers may stay underdone and collapse; if it runs hot, the edges can overbrown before the middle bakes. A reliable oven thermometer helps prevent these errors and gives you predictable results.
Prepare brownies according to the directions on the box. Fold in the peppermint baking chips.: Oil slicks will glisten on the tin surface, ensuring the cups release cleanly once they cool; this step preserves the round, domed shape of each cup. If you skip this, the brownie edges may cling and tear when you remove them. For extra insurance, I sometimes press a paper liner lightly into each cup, but the spray alone usually does the trick.
Use a large cookie scoop (3 tablespoons) to portion the brownie batter into the prepared muffin cups.: The batter should be glossy and slightly thick, with no streaks of flour; achieving the right viscosity matters because it affects how the batter bakes into a fudgy center. Stir until the mix is incorporated, avoiding vigorous beating which can introduce air and produce a cakier texture. A common mistake is over mixing, which makes the crumb drier and less tender.
Bake in preheated oven for 22-25 minutes. Remove pan from oven and place it on a cooling rack and allow the brownies to cool for about 15 minutes before removing them from the pan and to a wire rack to cool completely. I use a thin offset spatula to make this process a little easier.: You will see flecks of white and green throughout the shiny batter, and the chips will soften slightly from the batter warmth; folding preserves the chips’ shape and distributes mint evenly. Use a gentle folding motion to avoid toughening the batter. If you stir too aggressively, you risk breaking the chips into dust and overworking the batter.
When you're ready to serve up these Peppermint Cocoa Brownie Cups, top them with whipped cream, dust them with cocoa powder and sprinkle on the mini marshmallows and crushed candy canes.: The scooped batter will mound gently in each cup, offering consistent portions that bake at the same rate; visual uniformity helps all cups finish together. When the tin is full, the centers should rise slightly; uneven scoops cause some to bake faster and others slower. If your scoop sticks, lightly oil it between portions to keep the dollops neat.
Bake in preheated oven for 22 to 25 minutes: As they bake, you’ll notice the tops shift from glossy to matte and the aroma of warm chocolate will fill the room; look for the edges to set and a slight jiggle in the center when gently nudged. This timing creates a fudgy interior, while longer baking yields cakier cups. Opening the oven early can cause collapse, so resist peeking until near the end of the window.
Remove pan from oven and place it on a cooling rack and allow the brownies to cool for about 15 minutes before removing them from the pan and to a wire rack to cool completely: The warm brownie crumb will relax and firm up as it cools, making removal easier; the first cooling step prevents tearing and maintains shape. Transferring to a wire rack completes the cooling by allowing air to circulate. If you try to remove them when too hot, they may break apart, so patience here protects presentation.
I use a thin offset spatula to make this process a little easier: The spatula slides beneath the cups and gives you leverage without tearing, and you’ll feel the slight resistance ease as the cup lifts away cleanly. The thin blade prevents splintering and keeps edges intact. Avoid prodding with a fork, which can shred the surface and ruin the tidy cup look.
When you're ready to serve up these Peppermint Cocoa Brownie Cups, top them with whipped cream, dust them with cocoa powder and sprinkle on the mini marshmallows and crushed candy canes: The cool whipped cream contrasts with the still warm crumb if you decide to top sooner, and the cocoa powder adds depth while the mini marshmallows and crushed candy canes add playful texture; together they transform a simple brownie into a holiday worthy cup. Apply the toppings gently so the cup shape remains pristine. A common misstep is piling on toppings too early, which can cause marshmallows to melt or candy to clump; add delicate garnishes just before serving for best texture.