To make the hollandaise, sit a large
bowl over a pan of hot water and whisk
the egg yolks with 2 tbsp hot water.
Gradually add the melted butter (without
adding the milky liquid at the bottom) until
it has all been incorporated. Whisk in the
lemon juice and season with the cayenne
pepper and salt to taste, then set aside.
Heat a shallow pan of water with the
vinegar but no salt until gently boiling, then
poach the eggs for 2 mins. Remove with
a slotted spoon and cool in cold water.
Fry the spinach in a wok with a knob of
butter until wilted, then drain and season.
To serve, heat the grill to high. Lay the
muffins on a flat roasting tray, cut-side up,
then toast until brown. Butter the muffins
lightly, then top each with a ruffle of
smoked salmon. Divide the spinach
between the muffins, leaving a slight dip
in the middle to sit the eggs in. Spoon a
quarter of the sauce over each egg, then
return the tray under the grill to brown
for a min. Serve immediately.