Bake the sweet potatoes: Preheat the oven to 425°F. Line a rimmed baking sheet with foil. Poke holes all over sweet potatoes using the tines of a fork. Place on the baking sheet and bake for 45-60 minutes or until soft and tender. Reduce oven temperature to 375°F.
3 lbs. sweet potatoes (~ 3 large sweet potatoes)
Grease an oven safe 9x13 pan lightly with softened butter or baking spray. Set aside.
Brown the butter: For a detailed tutorial, see this post on how to brown butter. Add the vanilla bean to the brown butter, stir, and set aside. 4 Tbsp. unsalted butter, 1/2 vanilla bean pod, or 1 tsp. vanilla bean paste
Peel the sweet potatoes once cool enough to handle, discard the skins and place the sweet potato into a large bowl.
Beat the sweet potato in a stand mixer fitted with the whisk attachment, or use a hand mixer, for 1-2 minutes on medium speed, until nice and fluffy.
If the potatoes are still very hot, let cool down for a few minutes so the eggs dont cook. Once cooled, add the vanilla bean brown butter, eggs, buttermilk/sour cream, brown sugar and salt. Mix again until combined and then spread evenly in prepared baking dish.
1/2 cup buttermilk or sour cream, 2 Tbsp. dark brown sugar, 2 large eggs, lightly beaten, 1 tsp. kosher salt
Make the topping: mix the brown sugar, salt and cinnamon together in a medium sized bowl. Pour in the melted butter and stir. Add in the flour and pepitas. Stir until combined to form crumbs. The dough will hydrate to form those crumbs and then you can spoon this over the sweet potatoes.
1/2 cup dark brown sugar, packed, 1/2 tsp. ground cinnamon, pinch of salt, 4 Tbsp. unsalted butter, melted, 2/3 cup all purpose flour, 1/2 cup pepitas
Bake at 375°F for 30 minutes or until heated through. Serve hot and enjoy!
TO MAKE AHEAD: make the recipe as directed all the way up to step 6. Make the topping but keep the topping on the side, store in the fridge. Place the casserole in the fridge, covered, overnight until you're ready to bake. Prior to baking, place the topping on and bake for an additional 10 minutes or until hot since the casserole is now cold. Enjoy!