Lamb Shepherd's Pie Recipe

Name: Lamb Shepherd's Pie Recipe
Prep time: 35 min
Cook time: 25 min
Total time: 1 h
Cuisine: British
Ingredients: 2 and ½ lbs. Russet potatoes, peeled and cut into 1/2-3/4 inch dice; 1 Tbsp. + 1 tsp. salt, divided; 1 Tbsp. oil; 1 small onion, finely chopped; 2 cloves garlic, minced; 3 Tbsp. chopped rosemary, divided; 1 and ½ lbs. ground lamb; ¼ tsp. pepper; 2 Tbsp. flour; 1 cup beef broth (low sodium); 2 tsp. Worcestershire sauce; ¾ cup frozen peas, defrosted; ¼ cup butter; ¼ cup milk, heated; 1 tsp. lemon zest, optional