Preheat the oven to 200C/180 Fan/Gas 6.
Arrange the bacon on a baking tray and bake for 10 minutes, or until golden-brown and crisp. (Fry or grill if preferred.) Keep warm.
To make the hollandaise, whisk the egg yolks and white wine vinegar together in a medium bowl.
Sit the bowl over a pan of simmering water, making sure the bowl doesn't touch the water. Pour in the melted butter, whisking continuously until the sauce has thickened and is glossy. Season with salt and pepper. Cover with cling film and set aside.
To poach the eggs, bring the same water up to the boil, reduce to a simmer and add a dash of vinegar. Crack each egg into a ramekin or cup and swirl the water, then carefully tip the eggs into the pan.
Simmer for 3–4 minutes, or until the whites are just set but the yolks are soft. Using a slotted spoon, carefully lift the eggs out and drain on kitchen paper.
Toast the muffin halves and butter them. Divide between four plates.
Heat a frying pan, add the butter until melted and fry the spinach until wilted, season with salt and pepper.
Spoon the spinach on top of the muffins, top with the egg, spoon over some hollandaise and arrange a cross of two rashers on top. Serve hot.