1 1/2 (9-ounce) packages chocolate wafer cookies
5 tablespoons unsalted butter, melted and cooled slightly
3 8-ounce packages cream cheese, room temperature
1/2 cup powdered sugar
14 ounces milk chocolate, at least 35 per cent cocoa solids
1 teaspoon vegetable oil
4 ounces white chocolate
Heavy cream, to serve