French sandwiches with beef and onion spread

Ingredients:

Sandwiches

• 1 piece of roast beef weighing 1350 - 1800 g.
• 6 (15cm) French baguettes, halved lengthwise and lightly toasted
• 6 cloves of garlic
• Coarse salt and freshly ground black pepper
• 1 teaspoon olive oil
• 1/2 tsp celery salt
• A pinch of ground cayenne pepper
• 4 cups lightly salted meat broth
• 2 stalks celery, coarsely chopped
• 1 small onion, coarsely chopped
• 3 sprigs of parsley
• 2 tbsp (30 g) butter
• 2 tablespoons of wheat flour
• 2 tsp dry sherry

Onion paste

• 1 large onion, cut into thin rings
• 6 medium shallots, thinly sliced
• 2 bunches green onions, cut into rings (separate the white and green parts from each other)
• 3 tablespoons of vegetable oil
• Coarse salt
• 1.5 cups sour cream
• 1 cup mayonnaise
• 2 tsp white wine vinegar
• 2 tsp Worcestershire sauce

Preparation:

1. Prepare the onion spread: Heat vegetable oil in a skillet over medium-low heat. Add the onion and a pinch of salt; cover and cook, stirring occasionally, for 35 minutes, until golden brown.
   
   Add the white parts of the green onions and shallots; cover and continue cooking, stirring occasionally, until the onions are browned, about 25 minutes more. Stir in the green parts, remove from the heat, and let cool.
2. Chop the onion mixture and transfer to a bowl. Add sour cream, mayonnaise, vinegar, Worcestershire sauce, and 1 teaspoon of salt. Cover the onion spread with plastic wrap and refrigerate for 2 hours.
3. Prepare beef for sandwiches: Chop the garlic, then sprinkle with 1 teaspoon of salt and use the flat side of a knife to mash into a paste. Transfer to a bowl and toss with olive oil. celery salt, cayenne pepper, and 1/2 teaspoon black pepper. Make small slits all over the meat with a knife, then rub garlic paste into the slits. Wrap the meat in plastic wrap and refrigerate for 1 hour.
4. Remove the beef from the refrigerator an hour before cooking and leave at room temperature.
   
   Rub with 2 teaspoons salt and 1/2 teaspoon pepper. Place beef in a roasting pan; add 1 cup broth, 3/4 cup water, celery, onion, and parsley.
   
   Place the roasting pan in a preheated oven at 220°C (425°F) and bake for 10 minutes, then reduce the temperature to 180°C (350°F) and continue baking until a thermometer inserted into the center of the meat reads 46–47°C (115–118°F), about another 45 minutes.
   
   Transfer the beef to a cutting board and let it rest for 20 minutes. Strain the meat juices into a separate container and reserve for the sauce.
5. Prepare the sauce: Melt the butter in a saucepan over medium heat. Add the flour and cook for 1 minute. Add the meat juices and the remaining 3 cups of broth and bring to a boil, stirring constantly. Remove the saucepan from the heat and stir in the sherry.
6. Spread the baguettes with the onion spread. Slice the beef thinly across the grain. Toss the meat with the sauce, then arrange on the baguettes. Serve the French sandwiches with the remaining sauce.