Turkey Shepherds Pie

Name: Turkey Shepherd's Pie
Ingredients: 2 lb. sweet potatoes, peeled and cut into 1-in. chunks; 1 lb. parsnips, thinly sliced; 1/4 c. low-fat buttermilk; 1/4 c. plus 2 tbsp. olive oil; 1 medium onion, finely chopped; 2 cloves garlic, chopped; 1 tbsp. rosemary, chopped; 1 1/2 lb. lean ground turkey; 3 tbsp. Worcestershire sauce; 2 tbsp. tomato paste; 1 lb. frozen mixed vegetables; 3/4 c. lower-sodium chicken broth; 2 tbsp. cornstarch