Instructions

1. Place 3 cups mini marshmallows, 1/2 cup of the heavy cream, and 1/4 teaspoon kosher salt in a large microwave-safe bowl. Microwave on HIGH in 30-second bursts, stirring between each, until the marshmallows are fully melted, about 2 minutes total. (Alternatively, melt in a small saucepan over low heat.)
2. Set aside about 2 tablespoons semi-sweet chocolate chips from a 12-ounce bag for garnish. Immediately add the remaining chocolate to the warm marshmallow mixture. Stir until the chocolate is melted and the mixture is smooth. 
3. Set the chocolate-marshmallow mixture aside to cool until barely warm to the touch, about 30 minutes.
4. Place the remaining 2 cups cold heavy cream and 2 tablespoons granulated sugar in the bowl of a stand mixer fitted with the whisk attachment. (Alternatively, use an electric hand mixer or whisk and a large bowl.) Begin beating on low speed, gradually increase the speed to medium-high, and beat until stiff peaks form, 1 to 2 minutes.
5. Reserve and refrigerate about 1 cup of the whipped cream for topping the pie. Fold the remainig whipped cream into the cooled chocolate mixture until no streaks of cream remain.
6. Transfer the filling into a baked pastry crust or crumb crust and smooth into an even layer.
7. Refrigerate until the filling firms up, at least 1 hour and up to 3 hours. Top with the reserved whipped cream and chocolate chips.
8. Cut into slices and serve.