Preheat the oven to 375°F. Butter a 12-inch cast iron skillet or medium casserole dish and set aside.
Make the pumpkin layer: In a large bowl, whisk together pumpkin, sugar, eggs, pumpkin pie spice, salt, and vanilla. Whisk in the heavy cream until smooth. Pour into the skillet.
Make the crumble: In a medium bowl, whisk flour, sugar, cinnamon, and salt. Pour in melted butter and mix with a fork until crumbly. Sprinkle evenly over the pumpkin mixture.
Bake 40–45 minutes, until the filling is set and the top is golden. If the top browns too quickly, lightly cover with foil.
Rest 10 minutes, then serve warm with vanilla ice cream.