Preheat your oven to 375°F (190°C). Butter a 12-inch cast iron skillet or a medium casserole dish to prevent sticking and to help your dessert bake evenly. Set the prepared dish aside while you make the filling.

In a large bowl, whisk together the mashed sweet potatoes, 1 cup granulated sugar, eggs, pumpkin pie spice blend, 1/2 teaspoon salt, and vanilla extract until well combined. Pour in the heavy cream and whisk again until the mixture is smooth and creamy. Pour this filling evenly into your prepared skillet or casserole dish.

In a separate medium bowl, combine the all-purpose flour, 1 1/2 cups granulated sugar, ground cinnamon, and 1/2 teaspoon salt. Stir with a whisk to mix evenly. Add the melted butter, and use a fork (or hand mixer if you'd like) to stir until the mixture turns crumbly. I like to leave some bigger clumps in the streusel for extra texture—it gives the topping a delicious crunch!

Sprinkle the cinnamon streusel topping evenly over the sweet potato filling in your prepared dish, making sure the whole surface is covered. Transfer the dish to the oven and bake for 40 to 45 minutes, or until the filling is set and the top is golden brown.

Remove the casserole from the oven and let it cool for about 10 minutes to set the filling and make it easier to serve. Serve warm, topped with vanilla ice cream for an extra special treat. I find that the contrast of the hot casserole with cold ice cream is simply irresistible!