Place pretzels in a ziploc bag and crush with a rolling pin by rolling over them until they become fine crumbs.
Transfer pretzel crumbs into a bowl and stir in melted butter and brown sugar until combined.
Pour pretzel crumbs into a tart pan and firmly press into the pan until the bottom and sides of the pan are covered in a thick layer.
Bake for 10 minutes. Remove from oven and let cool completely on a wire rack before filling with ice cream.
In a medium bowl, let ice cream sit out at room temperature while the crust is baking. Stir with a spoon until ice cream is softened and creamy but not melted and liquidy. It should resemble soft serve ice cream.
Add peanut butter and stir until incorporated.
Scoop ice cream into pretzel crust. Spread and smooth the top with a spatula.
Whisk whipping cream and sugar together until cream thickens into firm peaks. Transfer to a piping bag fitted with a closed star tip and pipe rosettes on the surface of the ice cream.
Freeze ice cream pie for at least 4 hours or overnight before cutting and serving.