Directions

1. In a large mixing bowl, combie the beef and pork. Season with the salt and pepper. Mix gently by hand to combine, being careful not to overwork the meat or else the burgers will be tough.

2. Gently hand-form the ground beef into 4 big burgers about 1-inch thick. Don't pack the meat too tightly. Refrigerate the patties until you are ready to grill.

3. Combine the vinegar and 1/2 cup of the oil in a large bowl. Add the onion, pushing the slices down into the liquid. Set aside for at least 30 minutes or up to 2 hours, to pickle.

4. In a small pot, combine the remaining 1 cup oil and the garlic. Place over medium-low heat. Simmer the garlic gently for 20 to 25 minutes, or until tender when pierced with a knife. Remove the garlic from the oil and strain off any excess oil.

5. In a food processor or blender, combine the garlic and mayonnaise. Purée for 1 to 2 minutes, or until the garlic is well-incorporated and the mayonnaise is smooth. Place the aïoli in a small container and refrigerate. This may be made ahead and refrigerated for up to 5 days.
   

6. Brush a grill pan or a gas or charcoal grill with oil to create a nonstick surface. Preheat to medium-high.

7. Remove the onion from the vinegar and pat dry. Lay the onion on the grill and char for 3 minutes per side, being careful not to lose any of the slices in the grates when turning.

8. Grill the burgers for 8 minutes per side for medium. During the final 3 minutes, put a couple of slices of Brie on top of the patty to melt.

9. To assemble the burger, spread 1 tablespoon of roasted garlic aïoli on both halves of the pretzel rolls. Lay the burger on teh bottom half of the roll, cheese side up, and top with a quarter of the onions. Put a small pile of watercress on top and then the top half of the roll.