Place a mesh strainer over a medium sized bowl. Line with a dish towel and add shredded parsnips and sweet potato. Gather sides of dish towel together, keeping contents in the middle and squeeze until liquid seeps into bowl.
Drain liquid and return shredded vegetables to bowl. Add shallot, parsley, flour, egg, garlic powder, salt and pepper. Gently mix until well combined.
Lay four full-sized paper towels in a stack on a cutting board.
Heat oil in a heavy-bottomed pan over medium heat until sizzling. Using a 1/4 measuring cup or cookie scoop, scoop vegetable mixture into pan, leaving space between each to fritter flip. They should be about 2" in diameter.
Cook for about 2-3 minutes per side, until brown and crispy.
Transfer fritters to paper towel-lined cutting board to absorb any excess oil and sprinkle with flaky sea salt. Let cool slightly before transferring to a serving dish; garnish each fritter with a dollop of sour cream and fresh parsley.