01 - Preheat the oven to 350°F. Lightly grease a 9x9-inch baking dish or an equivalent casserole dish.
02 - In a large bowl, whisk together pumpkin purée, granulated sugar, brown sugar, eggs, milk, pumpkin pie spice, salt, and vanilla extract until smooth. Pour the mixture evenly into the prepared baking dish.
03 - In a separate bowl, combine flour, oats, brown sugar, granulated sugar, cinnamon, and salt. Add cold, cubed butter and blend with fingers or a pastry cutter until mixture resembles coarse crumbs.
04 - Sprinkle the crumble topping evenly over the pumpkin filling.
05 - Bake for 40 minutes or until topping is golden and filling is set but slightly wobbly in the center.
06 - Allow to cool for at least 20 minutes before serving. Serve warm or at room temperature, optionally with whipped cream or vanilla ice cream.