Preheat the oven to 325°F (160°C).
In a medium bowl, mix the coarsely ground walnuts, melted butter, and granulated sugar until the mixture is evenly moistened.
Press the walnut mixture firmly and evenly onto the bottom and up the sides of a 9-inch pie plate to form a crust.
Bake the crust for 12 to 14 minutes, or until the edges are golden; remove and let cool completely.
In a medium saucepan over medium heat, combine the chopped milk chocolate bars, mini marshmallows, and whole milk; cook and stir until the chocolate and marshmallows are melted and smooth.
Remove the saucepan from heat and let the chocolate mixture cool about 30 minutes.
In a medium bowl, beat the heavy whipping cream and vanilla with an electric mixer until soft peaks form.
Fold the cooled chocolate mixture into the whipped cream gently until combined, then scrape the filling into the cooled baked crust and smooth the top.
Spread the Cool Whip over the filling and sprinkle the chopped chocolate-toffee candy bars evenly on top.
Freeze the pie for about 8 hours or until firm.
When ready to serve, let the pie sit at room temperature 10 to 15 minutes before slicing.