Scrub the sweet potatoes and cut them in half. Pour 1 ½ cups of water into the Instant Pot and place the trivet in the bottom. Spread the sweet potatoes on top.
2 ½ pounds sweet potatoes, 1 ½ cups water
Secure and seal the lid. Cook the sweet potatoes on Manual High pressure for 18 minutes. When the time is up, perform a Quick Release of the pressure. When the pin drops, carefully remove the lid.
Remove the sweet potatoes to a cutting board and discard the water from the inner pot. When the potatoes are cool enough to be handled, slip the skins off and transfer them to a large mixing bowl. Mash them until smooth, then cool slightly.
Press Sauté on the Instant Pot. Add the butter. Once the butter melts, stir in the brown sugar, maple syrup, vanilla, cinnamon, ginger, and salt and simmer for 2 minutes, until melted.
3 tablespoons unsalted butter, ⅓ cup brown sugar, 2 tablespoons pure maple syrup, 1 teaspoon pure vanilla extract, 1 teaspoon ground cinnamon, ½ teaspoon ground ginger, ½ teaspoon kosher salt
To the mashed sweet potatoes, add the egg and heavy cream and mix well. Transfer this mixture into the inner pot. Cook for 1-2 minutes, stirring constantly, until heated through. Press Cancel.
1 large egg, 3 tablespoons heavy cream
Top with marshmallows and cover for 2-3 minutes, until they melt slightly (or use a kitchen torch to brown them). Top with pecans and serve.
1 ½ cups mini marshmallows, ¼ cup toasted chopped pecans
Optional: Prior to serving, transfer the sweet potato casserole filling from the Instant Pot to a 1-quart casserole dish. Top with marshmallows and pecans and bake at 350°F for 20-30 minutes, until melted and browned.