In a saucepan, add in the butter and brown sugar. Place over medium heat and let heat until the mixture becomes fluid and starts to bubble.
Add in 1/4 cup of the heavy cream and let it heat for another minute.
Remove from the heat and place in a mixing bowl. Place in the fridge for about 10 minutes.
Add in the powdered sugar, vanilla, and the 2 T. of heavy cream.
Beat on low until the mixture comes together.
Turn the beater on high and let it whip for 2 minutes. Place in a piping back with a large star tip.
Pipe swirls on the tops of the cooled cupcakes. The frosting won't be sticky, so work quickly adding the garnishes on.
Add on the caramel squares and M&M's®.