1-First, preheat your oven to 350°F and line a baking sheet with parchment paper or aluminum foil. Cut the butternut squash in half lengthwise, remove the seeds, and place it cut side down on the baking sheet. Bake for about 45 minutes or until it’s tender, then let it cool a bit before handling.

2-Next, grease a casserole dish with cooking spray to prevent sticking. Scoop the cooked squash flesh into a large mixing bowl, toss the skin, and mash it smooth with a potato masher or food processor. Stir in the whole milk, vanilla extract, sugar, melted unsalted butter, ground cinnamon, and salt until well blended.

3-Then, fold in the lightly beaten eggs, mixing just until combined it’s okay if there are a few lumps. Pour this mixture into your prepared casserole dish and bake for about 30 minutes until it’s almost set. While that’s baking, mix together the pecans or walnuts, melted unsalted butter, packed brown sugar, and ground cinnamon for the topping.

4-After the initial bake, sprinkle the topping evenly over the casserole and return it to the oven for another 15 minutes until fully set. If you’re adding marshmallows, bake for 45 minutes total, then add them and broil until golden and melted, keeping a close eye to avoid burning. Serve it right away for the best taste and texture.