Melt the white chocolate and butter over a double boiler over simmering water. Take off of the heat and whisk in sugar, eggs, vanilla, and peppermint extract. Whisk until smooth. Add flour and stir until combined.
Pour batter into a greased 9×13 pan that has been coated with cooking spray. Cook in a preheated 350 degree oven for 28 to 30 minutes.
As soon as you take the bars out of the oven, sprinkle with chocolate chips. Cool completely.
Start on the frosting. Melt the white chocolate and set aside to cool. Meanwhile, cream together butter and 1¾ cups powdered sugar. Beat in sour cream, vanilla, peppermint extract and salt. Beat on low until combined. Add the white chocolate and beat until smooth. Add the remaining powdered sugar and beat until light and fluffy.
Spread white chocolate frosting over cooled bars. Sprinkle with crushed peppermints.