To make the rosti, grate the potato into a clean tea-towel and squeeze any excess water out. Pop the potato into a bowl, season add the egg yolk and mix well. Divide into 4 and then form into a rosti shape.
Place a non-stick frying pan over a medium heat add the sunflower oil. Carefully place in the rosti and cook for 4-5 minutes before turning over. The rosti should be golden and crisp before turning.
While the rosti is cooking place a large pan filled with water about 3” deep for poaching the eggs with the vinegar. This water should be barely simmering.
For the Hollandaise, melt the butter in a jug, the microwave works very well. The butter must be hot.
Place the eggs and vinegar into a bowl and while whisking slowly pour in the melted butter a little at a time. Leave the white sediment in the jug. Add a squeeze of lemon juice and a tsp of hot water and leave until needed.
Cook the asparagus in a small saucepan of water for 3 minutes.
Crack the eggs into the water with the vinegar and poach for 3-4 minutes for a runny yolk.
To assemble place the golden crisp rosti onto the your plate, add the asparagus, followed by the poached egg and finally drizzle over the hollandaise sauce.
If you have a chefs ring place into the frying pan and press the rosti mixture in. This will give you a lovely professional look but certainly not essential.
There's an accompanying video to this method, check it out below. Explore wider potato recipe videos at our video hub.
For the rosti
500g Fluffy potatoes (such as Maris Piper or King Edward), peeled
2tbsp sunflower oil
1 egg yolk
Salt and milled pepper
For the Hollandaise
2 medium egg yolks
2tbsp white wine vinegar
1 tsp of hot water
12 asparagus spears, cut in half
4 large eggs
1tsp white wine vinegar