Heat oven to 250°F. Season roast with 3/4 teaspoon salt, 1/2 teaspoon pepper and 1 teaspoon oregano; place on a rack over a small pan and roast for 90 to 120 minutes until the center reaches 135–140°F.

Heat neutral oil in a heavy skillet over high heat and sear the roast for about 1 minute per side until browned. Check that the center reaches 145°F; if needed, return it to the low oven for 5 to 10 minutes, then rest for 10 minutes.

Cut the roast into two shorter pieces, put in a shallow container and refrigerate promptly for about 2 hours until cold and firm enough to slice thinly. Reserve the resting juices in the refrigerator.

Meanwhile, simmer vinegar, water, sugar and remaining salt in a small saucepan. Add cauliflower, carrot, celery and jalapeño, simmer for 3 minutes and cool for 20 minutes; drain, toss with olive oil and refrigerate.

Add stock, smashed garlic, remaining oregano and pepper, crushed red pepper and reserved beef juices to a saucepan. Simmer for 10 minutes, then strain.

Slice cold beef across the grain as thinly as possible. Warm the slices gently in the jus for 5 to 8 minutes until they reach 165°F, keeping the liquid below a hard boil.

Split and lightly toast the rolls. Lift beef into them with tongs, spoon about 1 tablespoon jus over each filling and add the drained quick giardiniera.

Close and serve one sandwich per person immediately, with extra jus separately for adding without soaking the sandwiches.