In a 2-cup liquid measure, stir broth, cornstarch, garlic, zest, juice, salt and pepper until cornstarch dissolves.
Melt 2 tsp butter in large nonstick skillet over medium-high heat. When butter just starts to brown, add scallops and cook, turning once, 4 to 5 minutes until golden and cooked through. Remove to a plate.
Add broth mixture to skillet; bring to a boil; boil 1 minute until slightly thickened. Remove from heat; stir in remaining butter and parsley. Spoon over scallops.