Make the hollandaise sauce. Melt the butter: Melt the butter slowly in a small pot. Try not to let it boil—you want the moisture in the butter to remain there and not steam away.

Blend egg yolks, lemon juice, salt, until lightened in color: Add the egg yolks, lemon juice, salt and cayenne (if using) into your blender. Blend the egg yolk mixture at a medium to medium high speed until it lightens in color, about 20-30 seconds.
The friction generated by the blender blades will heat the yolks a bit. The blending action will also introduce a little air into them, making your hollandaise a bit lighter.

Lower blender setting, slowly drizzle in melted butter: Once the yolks have lightened in color, turn the blender down to its lowest setting (if you only have one speed on your blender it will still work), and drizzle in the hot melted butter slowly, while the blender is going.
Continue to blend for another couple seconds after the butter is all incorporated.

Adjust salt and lemon juice to taste: Turn off the blender and taste the sauce. It should be buttery, lemony and just lightly salty. If it is not salty or lemony enough, you can add a little lemon juice or salt to taste.
If you want a thinner consistency, add a little warm water. Pulse briefly to incorporate the ingredients one more time.
Store until needed in a warm spot, like on or next to the stovetop. Use within an hour or so.

Strain thin whites with a fine mesh sieve: Place the raw egg into a fine mesh sieve over a bowl. The very thin egg whites will drain out through the sieve. Gently add to hot water: Then gently ease the raw egg into your pot of simmering hot water.

Toast English muffins: As soon as all the eggs are in the poaching water, begin toasting your English muffins. If you can’t get all the muffins toasted by the time the eggs are ready, gently remove the eggs from the poaching water and set in a bowl. Also add the spinach to a shallow pan with 2 tbsp of water and cook soft (wilted). Dry the spinach by putting it on rolling towel.