Melt the butter in a large pot over medium heat, then add the marshmallows and stir until starting to melt. Add ⅓ cup (80 g) of peanut butter and stir until completely melted. Remove the pot from the heat.
2. Step
Add the popcorn to the pot and stir to coat completely. Let cool for 2 minutes.
3. Step
Grease a 9-inch (23-cm) springform pan with nonstick spray. Press the popcorn mixture into the pan using the bottom of a measuring cup, creating an even layer along the bottom and halfway up the sides. Set aside.
4. Step
Add the dark chocolate chips and milk chocolate chips to a medium bowl and melt in the microwave, stirring every 30 seconds, about 2 minutes total. Set aside to cool to room temperature.
5. Step
In a separate medium bowl, whip the cream with an electric hand mixer until stiff peaks form, then add 3 tablespoons of powdered sugar and 1 teaspoon of vanilla and beat to incorporate.
6. Step
Fold the whipped cream into the cooled chocolate.
7. Step
Spoon the chocolate mixture into the popcorn crust. Spread evenly.
8. Step
In a small bowl, combine the remaining ⅓ cup (80 g) peanut butter, 1 tablespoon powdered sugar, 1 teaspoon of vanilla, and the milk, stirring until smooth. Transfer to a small piping bag or zip-top bag.
9. Step
Pipe lines across the surface of the pie. Drag a toothpick through, perpendicular to the lines, alternating directions from top to bottom.
10. Step
Chill the pie in the refrigerator for at least 4 hours.
