Place 3 egg yolks in a heatproof bowl with 1 tablespoon cold water; whisk for 1 to 2 minutes until the mixture becomes light and frothy. Place the bowl over a pan of barely simmering water - don't let the bowl touch the water because if the egg mixture gets too hot, they may scramble as they heat. Continue to whisk for another 1 or 2 minutes until warmed and slightly thickened. Slowly add cubes of softened butter, 1 at a time, whisking continually until mixture thickens. Season with salt and lemon juice. Transfer it to a heatproof jug and keep warm in a pot of warm (but not hot) water while you poach the eggs.
To poach the egg:
Bring a wide, deep pan of water and 1 tablespoon vinegar to the boil - the vinegar will help the eggs to set quicker. Lower the heat and use a spoon to stir the simmering water to create a swirl. Crack each egg into a separate ramekins or small bowls. Gently slide the eggs into the water, one at a time. Cook until the egg white has set but the yolk is soft and runny, about 2 minutes. Use a slotted spoon to carefully scoop out the poached eggs. Drain on kitchen paper to remove any excess water.
Butter the toast if desired, arrange ham on top of each slice, then top with a poached egg. Spoon or drizzle hollandaise sauce on top of the poached egg and garnish with some chopped chives.