Combine the chocolate chips, heavy cream, corn syrup and vanilla extract in a microwave safe bowl. Heat at 50% power for 1 minute, then stir with a whisk until the chocolate mixture is smooth and creamy. (If chocolates are not melting you can heat for an additional 15 seconds at 50% power). Pour the chocolate into the pre baked pie crust and smooth out into an even layer. Place in the freezer for 10 minutes.
Meanwhile prepare the peanut butter mousse by whisking together the instant vanilla pudding mix with 1 cup of cold milk until smooth. Heat the peanut butter in the microwave for just 10 seconds to loosen it up a bit, and then add it to the vanilla pudding. Whisk until smooth and thick. Gently fold in the thawed cool whip until fully incorporated. Pour on top of the chocolate layer.
If you'd like, decorate the top with chopped Reese's cups and a drizzle of chocolate. Keep stored in fridge until ready to enjoy.