Heat a large (over 12 inches) cast-iron skillet over medium-high heat. Add butter, and cook until melted and foamy, but do not let it brown. Add the lemon slices in a single layer and cook them undisturbed until they begin to brown, about 4 minutes.
Add the rosemary, red pepper flakes, garlic, lemon juice, Worcestershire and hot sauce, and bring it all to a simmer. Season the shrimp with salt and pepper then add them to the skillet. They should sizzle as they hit the pan. Cook, stirring and turning often, until they are pink and firm to the touch, about 3 to 4 minutes. Season with more salt and pepper. Serve with crusty bread and additional hot sauce at the table.