1. Brown the American lamb:
Set oven to 400°F. Add oil to a skillet set over medium-high heat. Add the ground lamb and break apart with a wooden spoon or spatula. Then, let it brown without disturbing it for a couple of minutes. Flip and cook until evenly browned. Remove from the pan and set aside.

2. Aromatics and mushrooms:
Wipe out any excess fat or burnt bits with a paper towel. Add the butter and saute the shallots for a couple of minutes or until beginning to be translucent. Add in the mushrooms and saute for 6-8 minutes or until liquid is released from the mushrooms and they are beginning to brown. Add in the garlic and cook for another minute.

3. Deglaze:
Move veggies to the side of the skillet and add in the tomato paste. Bloom and cook the tomato paste for about 1 minute until fragrant and then stir to combine everything. Add back in the lamb and sprinkle the flour, salt, pepper, and nutmeg over everything. Slowly add in the broth, stirring it in while scraping up any browned bits from the bottom of the pan. Add the bay leaf.

4. Simmer:
Simmer until the sauce is slightly thickened and then pour into an approximately 10x10 oval or rectangular baking dish. Cut the pastry into small rectangles and layer them over the top of the filling in the baking dish, trimming edges if needed.

5. Bake:
Brush with egg wash and bake at 400°F for 25–30 minutes, or until the pastry is golden and puffed and the filling is bubbling around the edges.