Line an 8x8" square pan with foil, extending the sides of the foil over the edges of the pan. Spray the foil with cooking spray and set aside.

In a large microwavable bowl, melt the white chocolate chips at 15-second increments on HIGH power until melted and smooth. If the mixture starts to get really thick and pasty, add in the cream. Do not over-heat. Alternatively, using the double-boiler method, place a pot of simmering water on medium-low heat and place a glass bowl on top, taking care to ensure the bowl does not touch the water. Melt the white chocolate over the double boiler until smooth, then proceed with the recipe as stated.

Fold in the vanilla extract and can of buttercream frosting until blended. Mixture will be very thick. Spread into the prepared pan, smoothing out the top. Top liberally with sprinkles.

Refrigerate for at least 2-3 hours or until firm before cutting into squares.