Unsalted butter
8 1/2 cups water
2 cups steel-cut oats
1 (14-ounce) can unsweetened coconut milk or 1 3/4 cups whole milk
1/4 cup packed light brown sugar
1/2 teaspoon fine salt
1 teaspoon vanilla extract
Coat the insert of the slow cooker with a thin layer of butter. Add the water, oats, coconut or whole milk, brown sugar, and salt and stir to combine.
Cover and cook on low until the oats are cooked through and creamy, about 7 to 8 hours. Stir in the vanilla and serve immediately.