Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking dish and set aside.

In a large bowl, combine the mashed sweet potatoes with melted butter, brown sugar, heavy cream, vanilla extract, salt, cinnamon, and nutmeg. I initially tried using milk, but found that heavy cream gave a richer texture.

Gently fold in the beaten eggs. I've always been apprehensive about using too many eggs, but for this dish, they're crucial for binding everything together.

Spread the sweet potato mixture evenly into the prepared baking dish. After a couple of trial runs, I found that smoothing the top with a spatula created a better surface for the streusel and marshmallows to sit on.

For the pecan streusel, mix the chopped pecans, flour, brown sugar, and salt in a separate bowl. Cut in the cold butter using a pastry cutter or your fingers until the mixture resembles coarse crumbs. A dear friend, who's a chef, once suggested using cold butter for that perfect crumbly texture, and it's been my go-to ever since.

Sprinkle the streusel evenly over the sweet potato mixture. Press down gently after each addition. This helps in achieving that beautiful, defined layer when you slice into the dish.

Bake in the preheated oven for 25 minutes. While I've always loved the traditional version, I once experimented by adding a hint of chili to the streusel, and it surprisingly elevated the dish to a whole new level.

Remove the casserole from the oven and sprinkle the mini marshmallows over the top. Return to the oven and bake for an additional 10 minutes, or until the marshmallows are golden brown. It took me a few tries to perfect the marshmallow topping. A common mistake is not watching it closely during these last minutes, so keep an eye on it to prevent burning.