Pour potatoes into large bowl and thaw about 1 hour.
While still very cold add onion and egg's, stir in eggs until blended.
Stir in baking powder, flour and salt.
Heat some oil in frying pan over medium heat.
Shape 1/2 cup in hand and place in oil, pack and shape gently with spatula.
Cook 15 minutes on each side. I like to cook mine slowly to ensure potatoes are cooked and evenly browned. The less they are moved the less they tend to fall apart. Check them gently every 5 minutes When browned evenly carefully flip them, repack with spatula and cook 15 minutes more.
Drain on paper towel 1 minute.
Transfer to warm serving dish (I like to keep mine in the oven set at 200°F).
Do several at a time, don't overcrowd, you will need to do them in batches.