Combine sweet potatoes, melted butter, sugar, milk, vanilla bean paste, and salt in a large bowl. Mash together thoroughly. If desired, use a hand mixer to achieve a smoother texture.
4 cups mashed cooked sweet potatoes, 4 tablespoons unsalted butter, melted, ⅓ cup packed brown sugar, ¼ cup milk, 2 tablespoons vanilla bean paste, ¼ teaspoon kosher salt, more to taste
Check seasoning, adding more salt if necessary. Scrape into prepared baking dish (or slow cooker) and heat as directed below.
Heat one of three ways:
Slow cooker: Spray the inside of a slow cooker with nonstick cooking spray and add the sweet potatoes. Heat on low for 2 to 3 hours or until heated through.
Microwave: Heat in microwave for 3 to 4 minutes, stirring 2 to 3 times, until heated through.
Bake: Heat in a covered glass baking dish in the oven at 325°Ffor 45 minutes, or until heated through.
Video
Notes
Cooking the sweet potatoes: Try cooking the sweet potatoes in your pressure cooker: Instant Pot sweet potatoes. See the post above for other cooking methods (baking, boiling, microwave).
Vanilla bean paste alternatives: Instead of vanilla bean paste, you may substitute 1 tablespoon of pure vanilla extract and the pulp (seeds) of two vanilla beans. Vanilla powder is more concentrated so use less, about 1½ teaspoons.
Possible add-ins:½ teaspoon freshly grated nutmeg, 1 teaspoon cinnamon, or 1 teaspoon finely grated orange zest.
Make ahead: Prepare the casserole as directed, but don't bake. Cover and refrigerate for up to 2 days. Bake as directed (or heat in slow cooker).