Place the sherry in a medium pot and bring to a boil, then lower the heat to a simmer and reduce to about 1/3 cup, about 10 minutes.
Meanwhile, preheat a large cast-iron skillet or griddle to medium-high heat. Heat another large skillet over medium-high heat with a drizzle of EVOO. Scatter the bacon in the pan and brown, then transfer to a paper-towel-lined plate to drain; leave the drippings in the pan.
Peel the potatoes and halve lengthwise. Slice each half lengthwise into 4 wedges, then crosswise into thirds (24 pieces per potato). Scatter the potato pieces in the bacon drippings and season with salt and generously with pepper. Cook to brown, about 5 minutes. Cover the skillet with foil, lower the heat and steam the potatoes, 6 to 7 minutes. Uncover, raise the heat to medium-high, flip and brown on the other side until deep, deep golden and very crisp, 3 to 4 minutes.
While the potatoes are working, place the beef in a bowl and season with salt (it makes a nice crust), the parsley, worcestershire, garlic, lots of pepper and a drizzle of EVOO. Combine but do not overwork. Shape into an even mound and score into 4 portions. Form the portions into mounds
Place the mounds in the preheated skillet and squish into patties with a spatula. Top with the shallots, pressing them in. Cook the burgers for 4 minutes, then flip and cook for 4 minutes more. Top with the stilton to melt in the last minute, then douse with the reduced sherry. Place cress on the roll bottoms, then the burgers, pickles and roll tops.
Stir together the sour cream, heavy cream, horseradish, chives, salt and pepper.
Serve the burgers with the pub browns topped with the horseradish sauce and bacon bits.