Add the heavy cream to a mixer with a whisk attachment and whip until soft peaks form. Gradually add the sugar then whip in the Mascarpone cheese until thickened. Cover and refrigerate.
Place the butter and brown sugar into a heavy pot and stir. Using a candy thermometer, heat and stir until it come to 300º F then remove from the heat. Line a cookie sheet with parchment paper and pour the toffee over in a thin layer. You'll see some separation of the oil from the butter and that's fine. Quickly and carefully add the pumpkin seeds to the toffee and sprinkle on some salt before it hardens.
Allow the toffee to sit for an hour then break up into shards.
Remove the pumpkin pie from the fridge and allow to come to room temperature.
Top the pie with the mascarpone whipped cream and toffee. Serve and enjoy!