Roast Beef and Camembert Panini with Arugula Aioli

Name: Roast Beef and Camembert Panini with Arugula Aioli
Ingredients: 1 tablespoon extra-virgin olive oil; 1 tablespoon unsalted butter; 1 medium yellow onion, thinly sliced; 2 sprigs fresh thyme; 1 bay leaf; 1 clove garlic, peeled and crushed; Kosher salt and freshly cracked black pepper; 1 cup mayonnaise; 2 cups packed arugula; 2 tablespoons fresh lemon juice; Kosher salt; 8 slices sourdough bread; One 8-ounce wheel Brie, thinly sliced; 1/2 pound sliced roast beef; 2 tablespoons extra-virgin olive oil