BBQ-Dipped Burgers with Ranch Slaw

Ingredients

• 1/2 cup sour cream
• 1/4 cup buttermilk
• 2 tablespoons super-fine sugar
• 3 tablespoons grated onion
• Juice of 1/2 lemon
• 2 tablespoons white vinegar
• 1 teaspoon celery salt
• 1 teaspoon black pepper
• 2 tablespoons each finely chopped dill, chives and parsley
• 1/2 pound white cabbage, thinly shredded
• 2 tablespoons butter
• 1/2 onion, finely chopped
• 2 large cloves garlic, finely chopped or grated
• 2 tablespoons tomato paste
• 2 tablespoons puréed chipotle in adobo
• 1 cup beef stock
• 1 tablespoon Worcestershire
• 1 tablespoon Tamari/soy sauce
• 2 scant tablespoons light brown sugar
• 1 1/2 pounds 80% lean ground sirloin
• Kosher salt and coarse black pepper
• Vegetable or olive oil, for drizzling
• 4 soft burger rolls with sesame seeds
• Sliced bread-and-butter or dill pickle chips
• 1/2 small white onion, finely chopped