In a large bowl, mix together mashed potatoes, cheeses, bacon, egg, flour, parsley, garlic powder, baking powder, salt and pepper.
In a large skillet, heat 2-3 tablespoons of oil over medium high heat.
Using a large cookie scoop, drop about ¼ cup of potato mixture into the hot skillet, 3-4 patties at a time. Flatten each potato mixture into a patty.
Cook for 3-4 minutes per side, or until nice and golden brown.
Transfer the cooked potato patties on to wire rack lined with paper towel to absorb excess oil.
Repeat with the remainder of potato mixture, adding more oil to the skillet as needed.
Serve hot with a side of sour cream, if desired. If not serving right away, you can keep the potato cakes warm in the oven at 200°F.