To make the hollandaise, place a large heatproof bowl over a pan of gently simmering water. Add the yolks to the bowl, whisk and slowly add the cubed butter, bit by bit. Whisk continuously until the sauce is combined and has thickened. Add the lemon juice, chives and a pinch of sea salt and stir through. Turn off the heat, but keep the bowl over the pan to keep warm.
To make the waffles, melt the butter in a small pan and add to a large bowl. Add the remaining ingredients and whisk together.
Pour the mixture into the waffle maker and cook for 6–8 minutes. If the waffle machine makes less than four at a time, repeat with the remaining batter and keep the cooked waffles warm in an oven set at a low temperature.
To make the poached eggs, bring a saucepan of water to the boil. Add the salt and vinegar and stir to dissolve the salt. Crack an egg into a cup and slowly lower the edge of the cup into the pot and drop in the egg. Cook the egg at a very gentle simmer for 3–4 minutes for the yolk to still be runny.
Remove the egg with a slotted spoon and place on a plate lined with kitchen paper. Repeat with the remaining eggs. Just before serving, reheat the eggs in warm water for 1 minute, if necessary.
To make the spinach, heat the butter in a saucepan, add the spinach and cook until wilted.
To serve, place a waffle on each plate with some wilted spinach on top. Top each with a poached egg and pour over the hollandaise sauce.