Cook bacon and asparagus and set aside. Toast English muffins; butter and set aside.
Next, poach the eggs. Add the water and vinegar to a large pot or saucepan and bring to a gentle simmer. Crack the eggs into eight individual ramekins or small bowls. Prepare an ice bath by filling a large bowl with cold water and a handful of ice cubes. Set aside. Gently swirl the water in your pan into a gentle vortex and slide an egg into the center of the vortex. Cook 2 to 3 minutes, gently stirring occasionally to keep the water moving, until the white is set and the yolk is soft. Use a slotted spoon to carefully transfer the egg to the prepared water bath. Repeat with the remaining eggs. You can poach 2 to 3 eggs at a time, but take things as slow as you need to ensure the eggs hold their shape and cook properly.
Make the sauce next. Add the egg yolks, lemon juice, Dijon mustard, salt and desired seasonings to a small blender. Blend about 30 seconds. The mixture should be very well incorporated and pale yellow in color. With the blender running, very slowly stream in the hot, melted butter until the hollandaise sauce is creamy, emulsified and has reached your desired consistency. For a thicker hollandaise, use 6 to 8 tablespoons butter. For a thinner hollandaise, use 8 to 10 tablespoons butter.
Top each toasted English muffin with toppings of choice. Place a poached egg on top. Finish with a spoonful of hollandaise sauce and garnish with parsley flakes, if desired. Serve immediately.