Sear the ground meat in a wide, oven-safe pan over high heat, breaking it up and letting it crisp. Remove and set aside.
In the same pan, cook the onions, carrot, celery and garlic until softened and translucent.
Return the meat to the pan with the tomato paste and season with salt and pepper.
Deglaze with the red wine, scraping up the browned bits from the bottom of the pan.
Pour in the beef stock, Worcestershire sauce and herbs. Simmer until thickened and saucy, then stir in the green peas.
Meanwhile, boil the potatoes until tender, drain, and pass them through a ricer or sieve for a smooth mash.
Warm the heavy cream with a pinch of saffron to infuse the color and flavor, then beat it into the potatoes along with the butter and salt until creamy.
Spread or pipe the mashed potatoes evenly over the meat and grate Parmesan generously over the top.
Bake at 400F until the top is golden and the filling is bubbling, about 25-30 minutes. Let rest a few minutes before serving.
Reconstructed from @cheffinwithzach's reel. He uses ground beef and, by his own admission, forgot the peas in the video (they are added back here). Amounts are approximate.
