In the INSTANT POT (preferred method): Place a rack in the instant pot and add 1 cup of water. Place the washed sweet potatoes on top of the rack. Cook on MANUAL (high pressure) for 15 minutes. Allow the sweet potatoes to natural release, until the valve drops on its own.
On the STOVE TOP: Place the sweet potatoes (whole and unpeeled) in a large pot and covering with water. Cover with a lid and bring to a boil. Boil for 10 minutes. then puncture each sweet potatoes 3 times. Boil for another 20-30 minutes until cooked through.
Meanwhile, preheat the oven to 350 F. Grease a 9x13 casserole dish. In a bowl, combine the pecans, flour, sugar, salt, and vanilla. Cut in the butter with a pastry cutter or mix with your hands until the mixture is sandy, with pea-sized chunks of butter. Set aside.
Peel the sweet potatoes and add them to a bowl with with the other filling ingredients. Use a hand mixer to whip the sweet potatoes until smooth. Taste and add more salt, sugar or milk as needed. (You may need to adjust the consistency/flavor based on how big your sweet potatoes are.) Whip the sweet potatoes until they are creamy and completely smooth.
Smooth the sweet potato filling into the prepared dish. Top with the pecan mixture. Bake for 25-30 minutes, until the top is golden and the sweet potatoes are bubbling. Let cool 10 minutes before serving. Enjoy!