Preheat the Oven
Preheat your oven to 350°F for silicone or nonstick pans, or 325°F if using metal pans.
Coat two 24-cup mini muffin pans with cooking spray to prevent sticking.
Prepare the Brownie Batter
In a large mixing bowl, prepare the brownie batter according to the package directions.
Scoop the batter into the prepared muffin cups, filling each about three-quarters full. You should get 28-30 mini brownies.
Bake the Brownies
Bake the brownies for 15 to 18 minutes, or until the edges are set but the centers remain soft and fudgy.
Remove from the oven and let them cool for 5 minutes in the pans.
Create Indentations
While the brownies are still warm, use the back of a small melon baller or a rounded 1/4-teaspoon measuring spoon to press a small indentation into the top of each brownie.
Let the brownies cool in the pans until they’re safe to handle (about 15 to 20 minutes), then transfer them to a wire rack to cool completely.
Make the Ganache Filling
In a small, microwave-safe bowl, combine the heavy cream and 2 oz. of chopped semisweet chocolate.
Microwave in 30-second increments, stirring after each, until the mixture is smooth and fully melted (about 2 minutes total).
Transfer the ganache to a small zip-top bag and snip off a small corner to create a piping bag.
Fill the Brownies
Pipe the ganache into the indentations on the brownie tops, filling each indentation generously.
Top each brownie with 3 to 4 mini marshmallows.
Refrigerate the brownies for 30 minutes to allow the ganache to set.
Add the Chocolate Drizzle
In another microwave-safe bowl, melt the remaining 2 oz. of chopped semisweet chocolate in 30-second increments, stirring after each, until smooth (about 3 minutes total).
Transfer the melted chocolate to a second zip-top bag and snip off a corner to create another piping bag.
Drizzle the melted chocolate over the tops of the brownie cups.
Decorate the Brownie Cups
Sprinkle the tops of the brownies with nonpareils and crushed peppermint candies (if using) for a festive touch.
Use the remaining melted chocolate as “glue” to attach the broken mini pretzel halves to the sides of the brownie cups, forming the handles.
Chill and Serve
Place the brownie cups in the refrigerator for 5 to 10 minutes to ensure the decorations and pretzel handles are secure.
Serve and enjoy your festive Mini Hot Chocolate Brownie Cups!