01 - Preheat oven to 350°F. Grease a 9×9-inch baking dish with butter or nonstick spray.
02 - In a large bowl, whisk together the pumpkin purée, granulated sugar, eggs, whole milk, heavy cream, pumpkin pie spice, vanilla extract, and salt until completely smooth. Pour the mixture into the prepared baking dish.
03 - In a medium bowl, combine the flour, brown sugar, rolled oats, cinnamon, and salt. Add the cold cubed butter and cut it in using a pastry cutter or your fingers until the mixture resembles coarse crumbs with pea-sized pieces.
04 - Sprinkle the crisp topping evenly over the pumpkin filling. Bake for 40 minutes, or until the topping is golden brown and the filling is just set with a slight jiggle in the center.
05 - Allow to cool for at least 15 minutes before serving. Serve warm or at room temperature, optionally topped with whipped cream or vanilla ice cream.