Test 3 - Shepherd's Pie with Mustard Thatch

NOTE 1: the main change is to reduce the amount of Worcestershire sauce.
NOTE 2: Create 'Topping' and 'Filling' sections.
NOTE 3: Changed instructions to add veg sooner; felt that following the old instructions meant the lamb was overcooking while veg (esp. carrots) weren't cooked yet. ALSO, added a pinch of salt to the potatoes to make the flavours pop.
4 - March 20, 2018: Followed the instructions, made it for a group, no improvements suggested.
5 - Feb 2 2019 - I think this is it. It is holding. Perhaps a pinch more salt in the potatoes.

Topping:
1lb 12oz floury (old) potatoes (weight is before peeling)
1/4 cup milk or cream
1 Tbsp Dijon mustard
1 Tbsp whole grain mustard
Butter, to taste
A couple of pinch of salt
Filling:
1 lb ground lamb
1 onion, chopped
2 celery stalks, sliced diced
2 carrots, diced
1 cup garden peas
1 Tbsp tomato paste
2 Tbsp cornstarch
2/3 cup stock (lamb or beef)
1 Tbsp tsp Worcestershire sauce
2 Tbsp chopped fresh rosemary (or 2 tsp dried and crumbled)
2 pinches salt
1\4 tsp pepper

1. Preheat oven to 400F.

Topping:

1. Boil the potatoes in lightly salted water until tender. Drain and mash until smooth, mixing in the dairy, mustards, butter, salt and pepper.

Filling:

1. Fry the lamb with a little butter. When you can start to hear the sizzle, add the vegetables and cook until just starting to brown, stirring often. Add the chopped vegetables and cook, stirring often, until lamb fully browns and veg start to cook, about 5 minutes. 
2. Add the tomato paste and the stock. Keep stirring and bring to a boil, stirring until the sauce thickens/reduces a bit, then remove from heat.
3. Stir in the Worcestershire sauce and the rosemary, and season to taste.

Assemblage:

1. Transfer the lamb mixture to a 7 cup ovenproof dish and spread the potato evenly on top.
2. Bake for 35 minutes or until golden on top.