Preheat your oven to whatever your packaging says. Grease one mini muffin tin and then grease the bottoms of another.
Prepare your brownie batter as directed on packaging and place in the oven. Bake as directed, undercooking by about 10 minutes. If you don't have cooking directions for using a mini muffin tin, start with 15 minutes. Check to see if the centers are cooked through, but still soft. you don't want these to over bake at all, but also don't want goo in the center. If they're too gooey, add another 2-3 minutes at a time, until the centers are set.
Once they come out of the oven, let them sit for 5 minutes. Then take your second muffin tin and press gently over the muffins to create the "cup." If you don't have a second mini muffin tin, you can take a spoon and create the indentation by pressing down gently. Takes a little longer, but it'll work too!
Then allow your brownies to fully cool on a wire rack.
Once they are cooled through, fill the cup with your favorite ice cream, then top with fudge and sprinkles or peanuts. You can get creative here!