1. Add mince and onion to searing slow cooker (or frying pan on stove top) to brown mince. Drain. Then add browned mince and onion to slow cooker bowl.
2. Add carrots, tomatoes, garlic, peas, tomato paste, celery, sauce, thyme, and beef stock and stir to combine.
3. Cook on HIGH for 1hr. While this is cooking prepare and cook potatoes as per step #4.
4. Peel and cut potatoes into large pieces and cook in a large saucepan of boiling water on stove until tender to fork. Drain and add milk and butter and mash to a smooth mashed consistency.
5. Use the back of a large wooden spoon/ladle to push down meat mixture in the base of slow cooker. Spoon mashed potato over meat base and smooth out with a metal spoon to achieve a flat finish.
6. Cover and cook on LOW for 3hrs.
7. Approx 30mins prior to serving add grated cheese on top of potato layer and then sprinkle top with paprika (it gives your dish the browned look on serving) and cover with tea towel for the last 30mins of cooking (between slow cooker and lid - see tea towel explanation here)
8. Serve with steamed broccoli or broccolini
**Note: Traditionally Shepherds Pie uses lamb mince, Cottage Pie uses beef. Feel free to choose which suits you best :)