Greek Yogurt Onion Dip

Ingredients

• 1 tablespoon olive oil
• 1 cup chopped shallots (about 2 large shallots; 1/3 pound)
• Kosher salt
• 1 teaspoon balsamic vinegar
• 1 cup 2-percent Greek yogurt
• 1/4 cup 1-percent milk
• 1/4 cup chopped fresh chives
• Freshly ground black pepper
• Cut-up vegetable sticks, low-salt pretzels or pita chips, for serving