Potato Pancakes with Gravlax and Dill

INGREDIENTS

• 1 small yellow onion (about 5 ounces), peeled and grated on the large holes of a box grater
• 3 Yukon gold potatoes (about 1 pound), peeled and grated on the large holes of a box grater
• 1 tablespoon chopped fresh dill, plus sprigs for garnish
• 1/2 teaspoon salt
• Pinch of freshly ground black pepper
• 1 large egg white
• 4 ounces gravlax
• 1/4 cup reduced-fat sour cream
• Olive-oil, cooking spray