Fill a large stockpot with water and heat over medium-high until boiling.

While water is heating, in a medium bowl whisk together egg yolks, lemon juice, water, and salt.

In a large saucepan, melt butter.

Add a spoonful of butter to the egg yolk mixture and whisk quickly.

Keep adding butter to the egg mixture while whisking until combined.

Transfer mixture back to the saucepan and cook, while whisking, until thickened.

Remove from heat and transfer to a heatproof bowl, covering the surface with plastic wrap.

Once water is boiling, add the vinegar and stir.

Poach the eggs 4 at a time for 3 1/2 minutes.

While the eggs are cooking, fry the potato cakes in a shallow pan of vegetable oil.

Remove eggs with a slotted spoon and place one on top of each potato pancake.

Coat each egg with the Hollandaise sauce.