Truly this is hands down the best gourmet sweet potato casserole ever! Once you make this version, you won't make another. This sweet potato casserole is a staple at every Thanksgiving dinner and my most requested recipe.
Preheat oven to 350°F and place oven rack in the center. Butter a 9X13 deep oven proof casserole and set aside.
Roast the sweet potatoes on a baking sheet until fork tender, about one hour. Insert a fork or knife to test. If the tester goes in and out without resistance, it's done. If you have resistance, check back every 15 minutes until you don't.
Remove from the oven and allow them to cool. Remove skin and combine with butter, white sugar, brown sugar, kosher salt, ground cinnamon and ground nutmeg in a large mixing bowl. Coarsely mash with a potato masher just to combined.
In a separate bowl, whisk beaten eggs, orange juice, vanilla extract and orange liqueur. Pour into potato mixture and combine.
Slowly mix in hot milk until it reaches the creamy consistency you desire. Taste and re-season, if needed. Pour and spread evenly into prepared 9X13 casserole. Set aside.
In a mixing bowl, whisk brown sugar, all-purpose flour, ground cinnamon, ground nutmeg and kosher salt.
Use a pastry cutter or a fork to cut in the butter into the dry ingredients until the butter is crumbly. Fold in chopped pecans. Refrigerate topping if not using immediately.
Spread the crumb topping evenly over the potato casserole and sprinkle with mini marshmallows, optional. Bake uncovered in a 350°F oven for 30 minutes or until base is bubbly and topping golden.
Remove from oven and allow to rest for 10-20 minutes before serving. Yields about 20 portions.
You can prepare each component a few days ahead and keep them separate. Place plastic wrap directly onto the potato mixture (so it doesn't create a skin) and store the crumb topping in a plastic zip bag. Thirty minutes before baking, set only the potato casserole on the counter to remove the chill. Remove plastic film, add crumb topping and marshmallows and bake accordingly. You could also roast the potatoes the day before to free up oven space on the big day. This dish is very easy to work with so any way you prep, it will work.
Note: You could also make the crumb topping with melted butter. Simply use a wooden spoon to gently stir and mix until you don't see any flour. It should look crumbly. Refrigerate until ready to use so the butter firms up.