Select sauté on the instant pot and adjust to normal. When the pot is hot, add in the pecans and let them sauté until they are slightly toasted. This should take about 6 to 7 minutes. Next remove the pecans and set them aside in a bowl.
Add in butter and let it sauté, until it melts.
Stir in the heavy whipping cream, maple syrup, ground cinnamon, kosher salt, ground black pepper, ground nutmeg, and vanilla extract. Keep stirring.
Add in the chopped sweet potatoes and give it a good stir.
Press cancel. And, secure the lid on the pot and select manual/high pressure for 14 minutes. When done quick release the pressure and open the lid.
Additionally, use a potato masher to the back of a ladle to mash the potatoes. Moreover, you can also use an immersion blender for super smooth potatoes. Season with additional salt and pepper as needed. Add in half the toasted pecans and mix well.
Scoop the sweet potato mash into a large baking dish and use a large ladle to smooth it out into a single layer. Next, top with the remaining pecans and the miniature marshmallows.
Set the temperature in your oven to broil at 375 and time to 2 minutes. Place casserole dish into oven and cook for 1-2 minutes, or until the desired color is reached. Make sure to watch it continually, it can burn quickly.