Here's one I've used
It is from the Cover and Bake cookbook by cook's illustrated. But I've summarized since they go into a LOT of detail.
1 1/2 lbs ground lamb
1 1/2 tsp salt
1 black pepper
2 med onions chopped coarse
2 med carrots pelled an dcut int 1/4" slices
1 garlic clove, minced
2 T all purpose flour
1 T tomato paste
2 1/4 c chicken broth
1/4 c full bodied red wine
1 t Worcestershire sauce
1 t chopped fresh thyme
1 t chopped fresh rosemary
1 c frozen peas, thawed
Topping:
2 lbs russet potatoes, peeled cut into 2" cubes
1 t salt
6 T unsalted butter
3/4 c whole milk
2 egg yolks
Filling:
Season lamb with salt and pepper and brown over med high heat (may need two batches). Remove lamb and set aside in a bowl.
Reduce heat to med and add onions and carrots. Cook till softened (4 min). Add garlic, flour, tomato paste and cook about 1 min. Whisk in broth, wine and Worcestershire sauce. Stir in spices and ground lamb. Bring to boil, reduce to simmer, cover and simmer 15 min.
Topping:
In separate sauce pan, Boil potatoes and 1/2 t salt for 15 - 20 min. Drain well and return to pan. Add rest of topping ingredients (I usually use 1/4 - 1/2 cup of milk not all).
Assemble and Bake:
Preheat oven 400 degrees. Stir peas into lamb mixture and check seasonings. Pour into 9X13 pan. With large spoon spread mashed potatoes over filling. Start at sides to ensure tight seal. Bake 20 - 25 min till golden brown. Allow to cool 5 - 10 min. serve.