To Steam the Sweet Potatoes (Instant Pot Method - Preferred):
Place a rack inside your Instant Pot and add one cup of water.
Arrange the washed sweet potatoes on top of the rack.
Set the Instant Pot to MANUAL (high pressure) and cook for 15 minutes.
Allow the sweet potatoes to naturally release, waiting until the valve drops on its own.
To Steam the Sweet Potatoes (Stovetop Method):
Place the sweet potatoes (whole and unpeeled) in a large pot and cover them with water.
Cover the pot with a lid and bring the water to a boil.
Boil for 10 minutes, then gently puncture each sweet potato three times.
Continue to boil for an additional 20-30 minutes, or until they are thoroughly cooked.
To Make the Casserole:
Preheat your oven to 350°F and grease a 9x13 casserole dish.
In a medium bowl, combine the pecans, flour, sugar, salt, and vanilla for the topping.
Cut in the softened butter using a pastry cutter or mix with your hands until the mixture achieves a sandy consistency with pea-sized chunks of butter. Set aside.
Peel the cooked sweet potatoes and place them in a large bowl with the milk, maple syrup, 1/4 cup melted butter, vanilla, cinnamon, nutmeg, salt, and the egg.
Use a hand mixer to whip the sweet potatoes until they achieve a smooth consistency.
Spread the sweet potato filling into the prepared dish.
Sprinkle the pecan crumble mixture evenly over the top.
Bake for approximately 25-30 minutes, or until the top is golden brown and the sweet potatoes are bubbling.
Allow it to cool for 10 minutes before serving to let the structure set.