- 5 tablespoons butter, divided
- 3/4 pound white or cremini mushrooms, sliced
- Salt and pepper
- 2 shallots, chopped
- 2 tablespoons thyme, chopped
- About 1 cup beef stock, divided
- About 1/3 cup HP sauce
- 2 tablespoons flour
- 2 teaspoons dry English mustard
- 1/2 cup lager beer, at room temp
- 1 1/2 cups shredded Cotswold or yellow sharp cheddar
- 1 tablespoon Worcestershire sauce
- A few dashes Tabasco
- 1 2-pound sirloin 1-inch thick, flat iron or flank steak
- Kosher salt and coarse black pepper
- 6 slices white bread, toasted, lightly buttered and cut into points corner to corner
- Watercress, large bunch
Preheat a cast-iron skillet or griddle to medium-high or high.
Melt 3 tablespoons butter in a large skillet over medium-high heat. When it foams, add mushrooms and brown. Season with salt and pepper, add shallots and thyme, and stir 2-3 minutes more. Stir in 1/4 cup beef stock and HP sauce; reduce heat to low.
Heat a saucepot over medium heat with remaining 2 tablespoons butter. When it foams, whisk in flour and dry mustard, and season with salt and pepper. Whisk in beer and remaining 3/4 cup beef stock, and thicken a bit. Add cheese in handfuls, stirring in a figure-eight motion with a wooden spoon to melt evenly. Season with Worcestershire and Tabasco; reduce heat to low.
Season steak with salt and pepper, and cook in the hot skillet or griddle for 8-10 minutes, turning once. Let rest 5 minutes then slice.
Arrange 3 toast points on each plate, top with sliced steak, HP mushrooms and Welsh Rarebit sauce. Garnish with watercress and serve.