1cupbutterunsalted and softened (if you're a beginner - margarine is not the same. It WILL NOT hold, in fact it will just be gross).
3cupspowdered sugardepending on the humidity/heat that day sometimes I have to add about 1/2 cup more, play around with it until you reach the consistency you desire
First things first: melt the chocolate. I prefer to pour the white chocolate chips in a glass bowl and place it over a pot of boiling water (double boiling), stirring constantly. If you are using Baker's Chocolate, chop it up first. The microwave is another option, but keep your eye on it and do 30 seconds at a time. Let cool to room temperature.
Place softened butter in a bowl and sift the powdered sugar over top. Starting slow, mix until incorporated and then beat until fluffy (about a minute or two).
After you have scraped the bowl, add the cream and vanilla. At this point you can now stir in the melted, cooled chocolate.
Turn your mixer to medium-high and beat for 3-4 minutes.