Bring a large pot of water to a boil and add your unpeeled, uncut sweet potatoes. Cook at a steady boil for approximately 30-40 minutes, or until a fork can easily piece the potato all the way to the middle.
Once the potatoes are cooked drain the water and run the potatoes under cool water until they are cool enough to handle.
Preheat the oven to 350 degrees F.
Cut potatoes in half and gently press on the end of the potato to push it out of the skin. You can also cut a slit in the side of the potato and just peel off the skin.
Place the peeled sweet potatoes in a large bowl and add the butter, salt, and orange juice. Beat with a hand mixer until fluffy.
Gently fold the pineapple into the sweet potatoes until well mixed.
Scoop the potato mixture into a greased 9x13 inch pan.
Bake at 350 degrees for 20 minutes. Stop and remove casserole from the oven and add a single layer of mini marshmallows. Place back in the oven and continue to bake until the marshmallows are lightly browned, approximately 5-10 minutes.
Remove from the oven and serve.