Thaw puff pastry according to directions and use a large cookie or biscuit cutter to cut four circles from each sheet of puff pastry.
Add puff pastry to a baking sheet lined with parchment paper and bake at 375 degrees for about 18-20 minutes until puffed and browned.
To make hollandaise, whisk together yolk, lemon, water, and salt. Set over a small pot of simmering water and whisk until steaming and frothy.
Start adding melted butter to yolk mixture about 1 tablespoon at a time, whisking furiously while you add. Continue to add melted butter until all the butter is used and sauce is silky and thick. Season with salt and pepper.
To poach eggs add about 1/3 cup of white vinegar to 1 gallon and bring to a simmer. Crack eggs, one at a time, into a small bowl. Swirl water with a slotted spoon and gently lower eggs into water. Depending on the size of your pot, you should be able to do at least 2 at a time.
Let eggs poach for three minutes (large eggs). Remove immediately with a slotted spoon and let drain briefly on a paper towel.
Split the puff pastry between four plates (2 per plate). Top each pastry with about an ounce of smoked salmon. Top each benedict with a poached egg and a drizzle of hollandaise sauce. Add capers and old bay seasoning as optional toppings.