Preheat the oven to 350°F and prepare the cake batter according to the directions on the back of the box.
Place a cone in each well of a 24-count mini cupcake pan and set aside.
Add 3 Tablespoons of cake batter into each of the cones, filling to just below the inside rim. You can spoon the batter in or use a small ice cream scoop to be more accurate. Do not overfill. If you do, the batter will spill over while cooking and make the rims of the cones soggy. Each cone may bake up a little differently in shape but they will look great as soon as you frost them!
Bake for 23 to 25 minutes or until a toothpick comes clean from the center of the cupcakes.
Allow them to cool completely, about 30 to 60 minutes.
Meanwhile, prepare the buttercream by creaming the butter in a large bowl or stand mixing fitted with a paddle attachment on loaw speed until pale and smooth.
Add in 3 cups of powdered sugar and 3 tablespoons heavy cream a little at a time, alternating between each, while mixing on low speed over the course of 3 minutes.
If your frosting needs a stiffer consistency, add the remaining sugar. If your frosting needs to be thinned out, add the remaining cream.
Add vanilla and salt and beat on medium-high speed for about 2 to 3 minutes until the frosting is light and fluffy.
If you want to make a twist frosting, remove half of the vanilla buttercream from the mixing bowl and set aside. To make the chocolate buttercream, add ½ cup of unsweetened cocoa powder and 2 tablespoons of vanilla extract to the remaining frosting and mix until incorporated.
Pipe the frosting into a swirl using a Wilton 2D tip and piping bag.
Add sprinkles on top for a fun garnish if desired!