Perfect Grilled Burgers

Ingredients

• 1 1/4 pounds 90/10 lean ground sirloin
• 1 1/4 pounds 80/20 lean ground chuck
• 2 tablespoons mayonnaise (such as Duke's)
• 1 1/2 tablespoons minced shallot (from 1 small shallot)
• 1 1/2 tablespoons Dijon mustard
• 2 teaspoons chopped fresh thyme
• 1 1/2 teaspoons kosher salt
• 1/2 teaspoon black pepper