In a large pan, heat the two tablespoons of oil over medium heat. Add onions and salt and cook, resisting the urge to stir, until they start to turn slightly brown, about 4-5 minutes. Once the onions start to colour, give them a light stir to release them from the pan. Turn the heat down to medium low. Repeat the process of letting the onions cook before stirring, cooking the onions for approximately 30-40 minutes or until they have reached a rich caramel colour. Set aside.
Caramelized onions can be made ahead of time and refrigerated, covered for up to a week.
Add salt and pepper to the grated potato and let sit for 3-4 minutes. Do not add water to potatoes. Heat a frying pan over medium-low heat with 2 tablespoons of oil. Remove 1/3 cup of potato for each cake, squeezing out excess water. Drop the potato into heated pan, forming a cake approximately 1 cm thick by 6 cm wide. Cook for 6-8 minutes on each side or until golden. Repeat until all the potato is cooked, adding more oil to the pan as needed. Keep warm until you are ready to serve.
In a blender, food processor or using a hand blender, blend the yolks, water, mustard, mayonnaise and lemon juice together. While the machine is running, drizzle in melted butter until well incorporated. Season with hot sauce or cayenne. Use immediately.
Heat a pan over medium heat. Drop greens into pan with a few drops of water and season with salt and pepper to taste. Mix greens lightly until they start to wilt. Remove from pan and reserve.
Bring a large pot of water to low simmer (190°F, 88°C), with vinegar added (1 tablespoon of vinegar for every 4 cups of water). First crack each egg individually into the bowl. Pour the egg slowly into water. Cook for 3-5 minutes, depending how well cooked you like your yolks. Remove the eggs using slotted spoon. Place on clean towel to remove excess water.
Place two potato cakes on each plate and top with a few wilted greens. Gently place one poached egg on each cake and drizzle each egg with 1 tablespoon of hollandaise. Garnish with caramelized onions and serve.
Once you’ve mastered poaching eggs, you can serve them on any base — various breads are common topped with your favourite greens, roasted vegetables, cured meats and cheeses.