Place in a medium saucepan and cover with cold water.
Set over high heat, cover and bring to a boil.
Once boiling, uncover, decrease the heat to maintain a simmer and cook until tender and a fork easily goes into the potatoes, approximately 10-15 minutes.
Place the half and half and butter into a microwave-safe container, and heat in the microwave until warmed, about 45 seconds.
Drain the potatoes in a colander and then return them to the saucepan.
Mash the potatoes and then add the half and half, butter, salt, and pepper and continue mashing until smooth. Stir in the egg yolk until well combined.
Meat Filling
Preheat the over to 400 degrees F.
While the potatoes are cooking, prepare the filling.
Place the canola oil into a 12" saute pan and set over medium-high heat.
Once the oil is hot, add the onion and carrots and saute until just browned and cooked through, approximately 3-4 minutes.
Add the garlic and stir to combine.
Add the ground beef, salt, and pepper and cook until browned and cooked through, approximately 3 minutes.
Sprinkle the meat with the flour and toss to coat, continuing to cook for another minute.
Add the tomato paste, chicken broth, Worcestershire, rosemary, thyme, and stir to combine.
Bring to a boil, reduce the heat to low, cover and simmer slowly 10-12 minutes or until the sauce thickens slightly.
Put It All Together
Add the corn and peas to the meat mixture and spread evenly into a 9 X 12-inch glass 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 half sheet pan on the middle rack of the oven and bake for 25 minutes or just until the potatoes begin to brown.
Remove to a cooling rack for at least 15 minutes before serving.
Notes
Scott's mother Anne used ground beef instead of the traditional ground lamb.