Cottage Pie With Mashed Yams

Name: Cottage Pie With Mashed Yams
Ingredients: 1 pound grass-fed ground beef; 1 cup homemade beef stock or store bought organic beef broth; 1/4 cup cream from grass-fed cows; 3/4 stick good quality Butter; 1 x large Onion, chopped; 1 cup frozen peas; 1 cup diced Carrots; 2 x medium sized yams or sweet potatoes; 3/4 cup shredded grass-fed sharp cheddar cheese; 1 tbsp arrowroot powder; 1 tbsp finely chopped fresh rosemary; 1 tsp dried thyme; 2 tbsp organic tomato paste; 1 tsp organic Worcestershire sauce; real sea salt and crushed black pepper to taste