Cut the potatoes into large chunks and place them in a 6-quart or larger Instant Pot. Add the water and then lock the lid, making sure the pressure valve is set to seal. Cook on high pressure for 8 minutes. Allow the pressure to release naturally for 10 minutes before manually removing the residual pressure.
Meanwhile, to make the topping, in a bowl, combine the pecans, marshmallows, sugar, butter, cinnamon and salt; set aside.
Carefully open the lid and mash with a potato masher until smooth. In a medium bow, whisk together the butter, heavy cream, maple syrup, vanilla, egg and spices. Pour into the potatoes and stir until combined. Press the sauté function on low and cook, stirring often, until bubbling, about 3 to 5 minutes. Turn off the machine and sprinkle the topping over the top of the potatoes. Serve immediately.