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.
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°F for 45 minutes, or until heated through.
Video
Notes
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.
Try cooking the sweet potatoes in your pressure cooker: Instant Pot sweet potatoes. See the post above for other cooking methods.
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).