Make the pudding: Melt white chocolate according to package directions (either in a microwave or double-boiler) until completely smooth. Set aside to cool slightly.

In a medium saucepan, sift cornstarch, sugar and salt. Slowly whisk in half-and-half, heavy cream and egg yolks. Whisk in milk and melted white chocolate.

Bring mixture to a boil over medium-high heat, whisking constantly. Reduce heat to medium; cook, stirring gently with a wooden spoon or spatula, 1 1/2 to 2 minutes until pudding coats the back of the spoon. Remove from heat; stir in butter and vanilla.

Pour pudding into a large bowl. Refrigerate uncovered 1 hour to 1 hour 15 minutes, stirring occasionally, until completely cooled.

Meanwhile, make the whipped cream: In a medium bowl with an electric hand mixer, beat heavy cream until stiff peaks form. Slowly beat in powdered sugar and vanilla until just combined. Refrigerate whipped cream until pudding is completely cooled.

Stir 1/2 cup crushed Oreos into cooled pudding. Gently fold in whipped cream until just combined. Pour or spoon pudding mixture evenly into 9-10 drinking glasses or dessert cups. Top evenly with remaining crushed cookies (about 1/4 cup each).

Cover cups and refrigerate at least 3 more hours up to overnight. Top each with 2 gummy worms just before serving.