Shepherd's Pie

I am not from the Northeast, and I first saw Shepherd's Pie at the Yankee Doodle Tap Room in the basement of the Nassau Inn in Princeton, where I would occasionally have dinner. I had known pot pies as a kid but these were far richer, more decadent, and far more delicious. Mette and I used to go to this Scottish pub in Pennsylvania called Braveheart and we enjoyed a passable Shepherd's Pie, but you can make one yourself that is damn near the perfect autumnal-winter's dinner. To be correct, as my friend Penn pointed out, a real Shepherd's Pie contains ground lamb. A similar pie containing ground beef or anything else is rightly called a Cottage Pie. However, being rebels, we will call this pie, made with ground beef, Shepherd's Pie, and we will love it.

1 1/2 lbs ground beef, pork, veal, or lamb
1 onion, diced
1 carrot, diced or sliced into 1/4 inch rounds
1 Tbsp tomato paste
1 clove garlic, minced finely (I now buy jars of minced garlic in olive oil)
1 Tbsp flour
1 cup chicken stock, low sodium if possible
1/4 c. red wine from last night
1 tsp Worcestershire sauce
1 bunch fresh thyme, leaves only
half a package of frozen peas (5 to 6 oz.; keep frozen)

2 lbs Russet potatoes (3 large), peeled and chopped into large dice (1/2 inch)
milk
butter
1 egg yolk

Season the ground beef with salt and pepper and brown gently in oil or fat. Remove and set aside. Add oil if needed to the pan and add onions and carrots plus a pinch of salt. Once the vegetables have softened, add the tomato paste and garlic and stir and cook for a minute or two. Add the flour, stir in well, and cook for another minute. Whisk in the liquids, the stock, wine, and Worcestershire, and mix everything together well, scraping up browned bits from the bottom of the pan. Add the browned meat and the thyme and simmer for a half hour.
Meanwhile, boil the potatoes in salted water and drain. Mash potatoes (or use a food processor). Stir in milk and butter as desired to make a creamy consistency. Stir in an egg yolk quickly so that it doesn't make scrambled eggs.
Preheat the oven to 400 F. Add the frozen peas to the finished meat mixture and combine well. Spoon the meat mixture into a pie pan and top with dollops of mashed potatoes. Using a fork, rake the potatoes across the top until they completely cover the meat mixture. Bake for about 30 minutes or until the potatoes begin to brown on top. Let rest for a few minutes and then cut and serve, preferably with a good beer.