Peel the potatoes and cut into quarters. Place in a medium saucepan and cover with cold water. Set over high heat, cover and bring to a boil. Once boiling, uncover, and lower the heat to medium, maintaining a simmer, and cook until tender, about 10 minutes. Warm the half-and-half and butter in a small saucepan.. Drain the potatoes in a colander and then return to the saucepan. Mash the potatoes and then add the half and half, butter, salt and pepper and continue to mash until smooth.
Add the peas to the lamb mixture and spread evenly into an oval baking dish. Top with the mashed potatoes, starting around the edges to create a seal to prevent the mixture from bubbling up and smooth with a rubber spatula. Place on a parchment lined baking sheet, and place in oven and bake for 25 minutes or just until the potatoes begin to brown. Remove and let cool for 10 minutes.
Recipe by Farmhouse 1820 at https://farmhouse1820.com/shepherds-pie/