In a medium saucepan combine butter and white chocolate chips.
Melt together over low heat, stirring. The butter and white chocolate will separate.
When everything is melted remove from heat and allow to sit for 15 minutes or so. Place saucepan in fridge and refrigerate until the mixture becomes solid, approx 3 hours. I actually let mine sit overnight.
When you're ready to prepare the frosting, remove from fridge and let it sit out at room temperature for 30 minutes or so, to take the chill off.
Place entire mass into bowl of stand mixer and beat for 2-3 minutes until frosting becomes light and fluffy.
Pipe or frost cupcakes or cake.
If made ahead, you can store at room temperature for up to a day. If stored for longer in fridge, you will need to whip the frosting again, as it will get solid.