Tear off marble-sized pieces of pie crust, and roll into small pebbles.
Combine pie crust pebbles and butter in a small bowl, tossing to coat.
In another small bowl, stir together sugar and cinnamon.
Add pie crust pebbles to cinnamon-sugar mixture, tossing to coat.
Spread the pie crust pebbles out on a small baking sheet.
Bake at 350 degrees for about 8 minutes, or until they are lightly browned on the bottom.
Stir them around to rotate a little, and return to oven for 1 minute.
Remove from oven, and cool completely -- cooling on the baking sheet is fine.
In a large mixing bowl, beat the heavy cream until stiff peaks form.
In another large bowl, whisk together sweetened condensed milk, pumpkin puree, vanilla extract, cinnamon, and pumpkin pie spice.
Gently fold the whipped cream and cooled pie crust pebbles into the pumpkin mixture until mostly combined. You can leave a few streaks if you'd like, or combine entirely -- up to you. But don't overmix such that the whipped cream deflates.
Pour mixture into a chilled 9x5-inch loaf pan or a similar size pan of any shape!
Cover with foil or plastic wrap, and freeze for at least 4 hours or until firm.