Generously coat the inside of a 6-quart slow cooker with nonstick cooking spray.
Nonstick cooking spray
Add the steel-cut oats, water, brown sugar and cinnamon. Stir to combine.
1 cup traditional steel-cut oats, 4 cups water, 1/4 cup packed light brown sugar, 1 tsp ground cinnamon
Wash the pears. Working from the bottom, carefully remove the cores and seeds, leaving the tops and stems intact. Leave the skins on.
3 large ripe Bartlett pears
Divide the butter among the pear cavities, gently pressing approximately 1 tablespoon into each of the 3 large pears. If using 4 small pears, divide the same 3 tablespoons among them.
3 Tbsp salted butter
Place the pears upright in the oatmeal mixture, with their stems pointing up.
Cover and cook on Low for approximately 7 hours, until the oats are tender and the pears are soft enough to collapse easily when pressed.
Add the vanilla. Use a potato masher to gently mash the pears into the oatmeal, then stir to combine. Remove all stems before serving.
1 tsp vanilla extract
Let stand for 5–10 minutes. Spoon into bowls and serve with your preferred toppings.