PREHEAT OVEN TO 250°. Wash but don't peel the sweet potato.
Shred potato on fine blade of a shredder or food processor.
Place in mixing bowl and set aside.
Finely chop ham; pulse using puree blade of food processor.
Add ham to the shredded potato. Add salt and pepper and mix well.
Heat 1 tablespoon butter in a non-stick 6-inch skillet over medium heat.
Add one-quarter of the potato-ham mixture.
Cook about 4 minutes, pressing down gently
to compact the hash as it cooks. Flip the hash patty and cook another 5 minutes.
Add more butter if necessary. Repeat with remaining mixture;
add more butter to skillet as needed. As each hash patty is done,
transfer to oven to keep warm. Place 2 poached eggs on each serving.
Garnish with a dollop of sour cream.