The Beefy Cheddar Recipe

Slice and heat pan

Thinly slice the yellow onions so they measure about 2 cups. Heat a large skillet over medium-low heat and add 1 tablespoon butter and 1 tablespoon olive oil until melted and shimmering.

Cook slowly

Add the sliced onions and 1/4 tsp kosher salt to the skillet. Cook, stirring every 2–3 minutes, over medium-low heat for 20–25 minutes. Allow onions to soften and begin to turn golden—adjust heat down if they start to brown too quickly.

Caramelize

After 15 minutes, sprinkle 1 teaspoon brown sugar over the onions and continue to cook, stirring, until deep golden-brown and richly flavored, about another 8–10 minutes. If they begin to stick, add up to 2 tablespoons water to deglaze the pan and scrape up browned bits.

Finish

Stir in 1 teaspoon apple cider vinegar, taste and adjust salt. Remove from heat and set aside. Total time for onions: about 30–35 minutes.

Prepare bread

Spread about 1/2 tablespoon softened butter evenly on one side of each sourdough slice (these will be the outside for grilling). On the interior (untoasted) side of two slices, spread 1 tablespoon prepared horseradish on each slice.

Layer sandwich

On the two horseradish-spread slices, divide the roast beef evenly (about 150 g per sandwich). Season the beef lightly with the remaining 1/2 teaspoon kosher salt and 1 teaspoon coarse black pepper, distributing evenly between the two sandwiches. Top the roast beef with the caramelized onions (divide evenly) and then place cheddar slices on top of the onions (3 oz per sandwich). If using, add a small handful (about 1/2 cup) of arugula or baby spinach over the cheese.

Close and grill

Place the remaining two bread slices on top, buttered side up. Heat a large skillet or griddle over medium heat. Add 1 tablespoon olive oil to the pan and place sandwiches buttered-side down in the skillet. Press lightly with a spatula or another pan. Cook 3–4 minutes until the bottom is golden brown. Carefully flip and cook the second side 3–4 minutes more, or until bread is golden and cheese is melted. If cheese is slow to melt, cover the skillet for 1–2 minutes to trap steam and speed melting.

Rest and serve

Remove sandwiches to a cutting board and let rest 1–2 minutes. Cut each sandwich in half on the diagonal and serve with pickle slices or a dill spear on the side if desired.