1. Preheat the Oven:

Preheat your oven to 375 degrees F (190 degrees C).

2. Brown the Lamb:

Place the olive oil and butter in a Dutch oven (or a large, heavy skillet) over medium heat.

Add the ground lamb and diced onion. Cook and stir until the meat is brown and crumbly, about 10 minutes. Break up the lamb with a spoon or spatula as it cooks.

3. Add Flour and Aromatics:

Stir in the flour until it’s incorporated into the lamb mixture.

Mix in the minced garlic, ketchup, minced fresh rosemary, paprika, cinnamon, salt, and black pepper. Cook and stir until the garlic is fragrant, 2 to 3 minutes.

4. Add Stock and Simmer:

Stir in the water, scraping up any brown bits from the bottom of the Dutch oven. These browned bits add a lot of flavor to the stew.

Reduce the heat to medium-low and bring the mixture to a simmer. Cook and stir until the sauce is thick, 5 to 6 minutes.

5. Add Vegetables and Transfer to Baking Dish:

Remove the lamb mixture from the heat.

Stir in the thawed peas and carrots until combined.

Spread the lamb mixture evenly into the bottom of a 9×13-inch baking dish. Set aside.

6. Cook and Mash the Potatoes:

Place the peeled and halved Yukon Gold potatoes into a large pot of salted water.

Bring the water to a boil over high heat. Then reduce the heat to medium and cook until the potatoes are tender, about 15 minutes.

Drain the potatoes well. Return them to the pot.

7. Make the Mashed Potato Topping:

Mash the Irish cheese, cream cheese, butter, and cayenne pepper into the potatoes until smooth.

Season with salt and black pepper to taste.

Whisk together the egg yolk and milk in a small bowl. Stir the egg yolk mixture into the mashed potato mixture.

8. Assemble and Bake:

Top the lamb mixture in the baking dish with the mashed potatoes. Spread the potatoes evenly to cover the filling completely.

Bake in the preheated oven until the top is golden brown and the sauce is bubbling up around the edges, 25 to 30 minutes.

9. Serve:

Let the Shepherd’s Pie cool slightly before serving. Enjoy!