Fill a medium pot with water and bring to a boil. Drop in the spinach and cook 3 minutes, stirring several times. Drain and place a bowl or plate directly on top of the spinach in the colander and press down to squeeze all excess water from the leaves. Cover and set aside.
Fill the bottom of a double boiler halfway with water and place over medium heat. Set the top pot over the water and drop in the egg yolk. Add the orange juice and whisk until blended. Whisk in the balsamic vinegar and lemon juice, then the turmeric, salt, and butter. Add 1 teaspoon of the dill and whisk until all ingredients are thoroughly blended and the sauce has a thick, creamy consistency (about 2 minutes).
Remove the top part of the double boiler and set aside. Pour the white vinegar into the water in the bottom pot and heat it to just under the boiling point. Gently crack the eggs one by one into the simmering water and poach for 3 minutes (I prefer my poached eggs a little firmer, so I cook them for 4 minutes). Remove the eggs with a slotted spoon and let the water drain from them. Transfer the eggs to a warm platter and cover.
Toast the English muffins, then place them on 6 plates. Place 1 tomato slice on each muffin half and spoon 1/4 cup of the cooked spinach on top. Top each with one poached egg, drizzle a spoonful of the sauce on top,. and sprinkle with the remaining dill and some black pepper (optional). Serve immediately.