Begin by making the potato topping. Peel the potatoes and cut them up into 1-2 inch sized pieces. Add them to a pot with 1 tablespoon of water. Bring to a boil and then reduce the heat to medium and cook for 15-20 minutes, or until the potatoes are tender. Once cooked, drain and set aside.
While to potatoes are cooking, make the lamb filling. Heat a large frying pan over medium-high heat. Once hot, add the ground lamb and onions and cook until the lamb is browned. Then add the Worcestershire sauce, tomato paste, 2 teaspoons of fresh thyme, and black pepper and mix to combine. Add the beef stock and reduce the heat to low. Simmer until the sauce has thickened then remove from the heat to let cool.
While the potatoes are still warm, mash them with a potato masher or a potato ricer so that they are smooth. Add the half and half, butter and cheese and mix to combine.
Preheat the oven to 400 degrees F.
Next, assemble the Shepherd's Pie. Add the lamb filling to the bottom of the dish and spread out so that it's in an even layer. Next, add the carrots, and then the peas, again in an even layer. Then top with the potatoes in an even layer.
For decoration, use the tines of a fork to add a design to the top of the potatoes. I simply drag the tines across the top to create lines across the pie. Next, sprinkle the pie(s) with the paprika for additional decoration.
Bake the Shepherd's Pie in the oven for 30 minutes, then serve immediately.