Boil the potatoes in a pot of salted water until they are tender.
This should take about 12 minutes.
Drain and mash them with butter, sour cream, and egg yolk until smooth.
Preheat a skillet over medium heat and add the EVOO.
Add the chopped onion, carrot, and parsnip.
Sauté these for around 5 minutes until they soften.
Add the ground lamb to the skillet.
Cook until browned, breaking up any lumps.
Sprinkle in flour, stirring for about a minute to combine.
Pour in the beef broth and stir.
Let it simmer until the mixture thickens, about 5 more minutes.
Season with salt and pepper to taste.
Spread the meat mixture in an oven-safe dish.
Top it with the mashed potatoes evenly and place under a broiler until the top is golden brown, about 5 minutes.