French Dip Sandwich

Combine the onions, 8 g fine salt, butter, and 50 ml water in a Dutch oven, cover and cook over medium heat, stirring every 5 minutes, until softened (10–15 min).

Uncover and continue cooking over medium‑low heat, deglazing with small splashes of water as needed, until a deep caramel color develops (35–50 min).

In a separate pot combine beef stock, Worcestershire sauce, Better Than Bouillon, and 5‑8 g salt; whisk in gelatin until dissolved, bring to a simmer and reduce by about 30‑40 % (≈10 min).

Mix mayonnaise, sour cream, prepared horseradish, and 3 g salt together to form the horseradish sauce.

Preheat the oven to 400°F (400°F). Slice the hoagie rolls, place them on a sheet pan and toast for 5 minutes.

Add two provolone cheese slices to each bottom half of the rolls and return to the oven for 3‑4 minutes, until melted and bubbly.

Heat the reduced jus to about 135°F (135°F). Quickly dip the roast‑beef slices in the jus for 20‑30 seconds, then layer the beef, warm caramelized onions, and horseradish sauce on the cheese‑topped rolls.

Close the sandwiches and serve immediately with the remaining hot jus for dipping.