Absolute Best Roast Beef Sandwich

1/2 cup good-quality sour cream

1 tablespoon prepared horseradish

2 tablespoons unsweetened all-natural applesauce

2 tablespoons panko or plain breadcrumbs

2 tablespoons finely chopped chives

Salt and coarse black pepper

8 slices white or peasant bread from a large round loaf

8 slices rare roast beef or about 2/3 to 3/4 pound thinly sliced leftover steaks of any cut

1/4 cup minced red onion or 1 large shallot, finely chopped

A handful flat-leaf parsley, very finely chopped

1 small red chile pepper, such as fresno or cherry, seeded and finely chopped

Zest of 1 lemon

1 small bunch watercress–trimmed, cleaned and dried

1/2 pound brick of the sharpest white cheddar available to you, thinly sliced (itll be crumbly if its very sharp)

 

Combine the sauce ingredients. Heat a panini press, cast-iron skillet or griddle over medium to medium-high heat.   On a work surface, spread the horseradish sauce liberally over 4 slices of bread. Arrange 2 slices of rare roast beef over the sauce. Combine the red onion (or shallot) with the parsley, chile pepper and lemon zest and sprinkle liberally over the roast beef. Arrange a layer of watercress over the beef. Divide the cheese evenly among the sandwiches and set the remaining bread slices in place. Press the panini 2 at a time on the panini press or in a hot skillet with a pan weighted on top.