Place cauliflower in a large saucepan and add just enough water to cover. Add a good pinch of salt to the water. Bring water to a boil over high heat and cook, uncovered, 10 minutes, or until cauliflower is tender.
Using a colander, thoroughly drain the water from the cauliflower. Transfer to large bowl and using a fork or potato masher, mash up the cauliflower.
Stir in the diced onion while cauliflower still hot to soften onion.
Add in egg yolks, parsley, salt, and pepper.
Sprinkle in flour and stir until combined.
In a separate bowl, whisk egg whites until soft peaks form.
Fold into cauliflower mixture.
In a large nonstick skillet, add enough oil to cover bottom of skillet and place over medium high heat.
When the oil starts to ripple, spoon in enough batter to form a pancake about 3 - 4 inches in diameter.
Cook until golden brown and set - about 3 minutes per side.
Transfer to a baking sheet lined with paper towels and place in oven to keep warm.