Grilled Steak and Peppers Vinaigrette

INGREDIENTS

• Equipment: a large (2-burner) grill pan
• 1 large bunch leeks (2 to 3 pounds; white and pale green parts only)
• 2 tablespoons red-wine vinegar
• 2 tablespoons Dijon mustard
• 5 tablespoons extra-virgin olive oil
• 1 3/4 cups reduced-sodium chicken broth
• 2 pounds sirloin flap steaks
• 2 tablespoons unsalted butter
• 2 tablespoons plus 2 teaspoon olive oil, divided
• 3 thyme sprigs
• 1 Turkish or 1/2 California bay leaf
• 4 Cubanelle peppers (Italian green frying peppers)