Preheat oven to 400°. Bake sweet potatoes at 400° for 1 hour. Peel potatoes and place in bowl of electric mixer. Reduce temperature to 325°.
Beat the sweet potatoes with butter, milk, eggs, vanilla, and salt until smooth. Set aside.
Use a 2" round cookie cutter or fluted ravioli cutter to cut out 24 mini pie bites. Press them gently into a mini muffin tin sprayed with cooking spray.
In a separate bowl, combine pecan topping ingredients (butter, brown sugar, flour and pecans). Stir to combine.
Fill each pie shell with sweet potato casserole filling. Top half with pecan topping and other half with marshmallows.
Bake for 20-30 minutes or until pie shells are lightly golden.
Notes
You'll have leftover filling, so if you're making these bites for a large crowd, use two more refrigerated pie crusts to make 48 bites.