For the brownie part melt your white chocolate and butter either in the microwave or a double boiler.
White Chocolate burns easily so be sure and watch it. Melt it in small increments of time. Whisk in eggs and vanilla and then add in sugar.
Add in flour and stir to combine.
Put into a greased or parchment lined 9 x 13 pan.
Bake for 25-30 minutes. Cool and then frost. They are done when a toothpick comes out clean.
Melt butter and white chocolate in microwave or double boiler.
Remove from heat and add powdered sugar, whipping cream and vanilla. Stir until smooth
White Chocolate can be a bit temperamental when melting. It burns very easily so be sure and take it low and slow when melting your white chocolate, especially if you are doing it in a microwave. I often use a double boiler to melt my chocolate so I have a bit more control.
I like to line my pan with parchment paper or aluminum foil as it makes it easier to remove the brownies from the pan. Just lift up on the paper to remove the brownies from the pan.