For the hollandaise: Melt the butter in a small saucepan over medium heat (or in the microwave). Combine the yolks, chives, lemon juice, salt and pepper in a food processor or blender and pulse to incorporate. Slowly drizzle the hot butter into the blender until the sauce is thick and creamy. Pour the sauce into a small bowl and set aside.
For the stuffing cakes: Place the stuffing in a large bowl, and mix to break up any large clumps. Add the eggs and stir well to combine, making sure the eggs are mixed in. Scoop 1/3 cup of the stuffing into your hands and shape into a patty, about 3-inches wide and 1/2 inch thick. Repeat to make 6 stuffing cakes. Heat the oil in a heavy skillet over medium-high heat and cook the cakes until golden brown, 2 to 3 minutes per side (do this in batches if necessary). Transfer to a paper-towel-lined plate and repeat with the remaining cakes. Loosely cover with foil to keep the cakes warm.
Heat oven to 375 F. Arrange the pancetta in a single layer on a foil-lined baking tray and bake until browned and crispy, about 7-10 minutes. Transfer to a paper-towel-lined plate.
To assemble, fill a deep, wide skillet with water, not quite to the top and bring to a full boil. Meanwhile, crack each egg into a little cup or ramekin and set aside. Once the water is at a full boil, turn it way down until it’s just barely simmering. Add a big pinch of kosher salt (about a 1/2 teaspoon) and the vinegar. Give the water a stir to combine.
With the handle of a wooden spoon, swirl the water in a tight little circle and drop the first egg right in the middle. You can use the wooden spoon to kind of coax the white in a little bit but don’t be too stressed about it. It will come together, I promise. Do the same with the other eggs, leaving as much space as possible between each one.
Let them poach in the gently simmering water for about 3-4 minutes. Using the slotted spoon, scoop one up, and check it for doneness. For me, a perfect poached egg has a fully set white and a very runny yolk. If you like your yolk more set, let it cook a minute or so longer. Once it’s done to your liking, gently remove them and set on a paper towel to drain.
Repeat with the remaining eggs. To serve, place one stuffing cake on a plate. Top with a slice of pancetta, a poached egg and a generous drizzle of hollandaise sauce.