Bacon Burgers on Brioche Buns

Preheat the oven to 400 degrees F. On a rimmed baking sheet, toss the onions with 2 tablespoons of the olive oil, and roast until softened, about 20 minutes.

Meanwhile, in a small bowl, whisk the mayonnaise with the lemon juice. Gradually whisk in the remaining 1/4 cup of olive oil and season with salt and pepper.

In a large skillet, cook the bacon over moderately high heat until crisp. Drain on paper towels and break each strip in half.

Light a grill or preheat a grill pan. Form the ground meat into eight patties. Season generously with salt and pepper, and brush with olive oil. Grill over moderately high heat until well-browned on the bottom, 5 minutes. Flip the burgers, mound the brie on top, and grill for 4 minutes longer, until the cheese is slightly melted and the burgers are medium-rare.

Spread the lemon mayonnaise on the cut sides of the buns. Set the burgers on the bottoms and top with the bacon and onions. Close the burgers and serve right away.