For the filling: Preheat the oven to 425 degrees. Line a baking sheet with foil. Place the sweet potatoes on the foil and pierce the tops 2-3 times with a knife. Loosely cover with foil. Roast until very soft, about 50-60 minutes. Uncover and let rest until cool enough to handle. Peel the sweet potatoes, discarding the skin.  In a large bowl, combine the roasted sweet potato, butter, cream, light brown sugar, eggs, salt, cinnamon, smoked paprika and cayenne. Mash until smooth (or leave it a little chunky if you like!)  Reduce the oven temperature to 375 degrees. Butter a 9x13-inch casserole dish. Place the sweet potato filling in casserole dish and smooth the top. For the topping: In a small bowl, stir together the flour, sugar, cinnamon, and salt. Add the pecans and butter and mix until the mixture is clumpy. Sprinkle 1 cup of marshmallows all over the potato filling.  Then top with all of the streusel. Bake at for 25 minutes. Remove from the oven and top with the remaining 1 cup of marshmallows. Return to the oven for 10-15 minutes until the casserole is bubbly around the edges, hot in the middle and the marshmallows on top are golden brown. Let cool for a few minutes before serving.