To make the Herb-Roasted Potatoes: Remove them from the oven and cover to keep warm. Turn the oven heat up to broil. Put the English muffin halves on a baking sheet and brown on both sides under the broiler. Remove to a plate. Reduce the oven heat to 200 degrees F and put the English muffins in the oven to keep warm.
Heat 2 to 3 inches salted water to a simmer in a wide saucepan or deep skillet for the eggs; turn off the heat and cover to keep warm.
Meanwhile, make the hollandaise. Combine the egg yolks, lemon juice, water, salt and cayenne in a blender and blend until light and fluffy, about 1 minute. Then, with the blender going, drizzle in the melted butter in a thin stream. Taste for salt and lemon juice. To keep the sauce warm, put the whole blender jar in a bowl of warm water; set aside while you finish the dish.
When the potatoes are out of the oven, heat a 2-count of olive oil a large skillet over medium-high heat. Add half of the bacon slices and brown on both sides. Transfer to a plate lined with paper towels. Brown the remaining 4 slices and put the on the plate. Put the bacon in the oven to keep warm.
Put the skillet back over medium heat. Add a 2-count of olive oil. Add the onion and cook until softened, 3 to 5 minutes. Add the spinach and give it all a stir; cook until warmed through, 3 to 4 minutes. Stir in the cream and simmer to reduce. Season with salt and pepper.
Return the water to a bare simmer. Add the vinegar and swirl a couple of times with a kitchen spoon. Then, first cracking each egg into a cup, gently drop 4 eggs into the simmering water and cook until just set, 3 to 5 minutes.
Meanwhile, get yourself 4 serving plates and put 2 muffin halves on each plate. Put a piece of bacon on each half and top with a spoonful of spinach. Remove the poached eggs with a slotted spoon and place on top of the spinach. Do the same with the remaining 4 eggs. Spoon the warm hollandaise sauce over and garnish with a parsley sprig. Serve with the Herb-Roasted Potatoes.
Preheat the oven to 375 degrees F. Toss together the potatoes, oil, and thyme, and sprinkle with salt. Dump the potatoes out on a baking sheet and roast until tender and crisp on the edges, 30 to 40 minutes.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.