Step 1 In a microwave-safe bowl, heat the white chocolate in 15 second increments, stirring in between, until melted and just warm. Stir until smooth. (The white chocolate can also be melted in a bowl set over a pot of simmering water, stirring until melted and smooth; remove from heat before continuing.)
Step 2 Slowly whisk in the heavy cream until combined. Whisk in the peppermint extract. Refrigerate the filling until cool and thick but not hard to the touch. It needs to have a spreadable consistency. This makes a scant 1½ cups ganache.