Prepare the Meat Layer: Season the ground lamb with 1 tsp salt. Place it in the slow cooker, spreading it out to form an even layer. Cook on low for 3-4 hours until the meat is fully cooked and starts to brown a little on the edges.
Prepare the "Topping": Whisk together the egg yolks, heavy cream, and 1/2 tsp salt until well combined.
Assemble the Pie: Once the meat layer is cooked, carefully pour off any excess fat. Spread the egg yolk mixture over the meat in the slow cooker. If using, sprinkle the shredded cheese on top of the egg mixture.
Cook the Pie: Continue cooking on low for 1-2 hours, or until the topping is set and, if using cheese, it's melted and slightly golden.
Serving: Let the "Shepherd's Pie" rest for a few minutes after cooking. Then, serve it directly from the slow cooker.