FOR THE HOLLANDAISE:

1. Add egg yolks, lemon juice, and salt to a tall, narrow cup that fits the head of an immersion blender. (I use this method for foolproof hollandaise - watch the video for a tutorial!)
2. Melt butter in a saucepan (or in the microwave!) until a thermometer registers the butter temperature at at least 200 degrees F.
3. Blend the egg mixture with the immersion blender until egg yolks have lightened in color. Stream hot butter in a little at a time while you run the immersion blender, letting the hot butter cook the eggs and blending until hollandaise is light and fluffy and all butter has been incorporated. If the hollandaise gets too thick, blend in a few teaspoons of water to loosen it before serving.
4. Side note: you could also make this hollandaise in a regular blender if you don't have an immersion blender. I just like the ease of the immersion blender!

TO ASSEMBLE:

1. Poach each egg in hot water (water should be just barely simmering for best results) until egg whites have cooked through, about 4 minutes.
2. While eggs are poaching, toast sourdough slices (in the toaster works fine!)
3. Top each toasted sourdough slice with a slice of mozzarella cheese and a slice or two of tomato. Hit the tomatoes with a pinch of salt and pepper.
4. When eggs are cooked, remove them with a slotted spoon and place one egg on top of each toast-cheese-tomato stack. Top the eggs with another pinch of salt and pepper.
5. Cover each Eggs Benedict stack with a generous pour of hollandaise, then top with chopped basil. Garnish with an extra basil leaf if desired and serve immediately.