Sauté onion, then add meat and spices, brown. Heat olive oil in a large skillet over medium heat. Add the chopped onion and cook until softened, about 4–5 minutes. Add ground venison, rosemary, thyme, salt, and pepper. Cook, breaking it up with a spatula, until browned.
Cook the potatoes while the meat browns. Place peeled and chunked potatoes in a large pot. Cover with water and add a generous pinch of salt. Bring to a boil, then reduce heat and simmer until fork-tender, about 15–20 minutes.
Add your butter, salt, and cream, mix with hand mixer. Drain the potatoes and return to the pot. Add butter, heavy cream (or half and half), salt, pepper, and 1 tablespoon of chopped parsley. Use a hand mixer or potato masher to whip until fluffy and smooth.
Once meat is browned, add Worcestershire, flour, tomato paste, and broth. Stir in Worcestershire sauce, flour, tomato paste, and beef broth. Simmer over medium heat for 4–5 minutes, stirring occasionally, until slightly thickened.
Add corn and peas, stir in well. Stir in frozen corn and peas. Let cook for 1–2 minutes to heat through. Remove from heat.
Top with mashed potatoes, sprinkle with Parmesan, and bake. Spread mashed potatoes over the top of the meat mixture and smooth out. Sprinkle with grated Parmesan cheese. Bake in a preheated 400°F oven for 25 minutes, or until the top is golden and the filling is bubbling around the edges.
Top with remaining parsley and serve.
Notes
Err on the thicker side when making your mashed potatoes. If they are too runny, they won't sit on top of your meat mixture very well.
This is a great recipe for using up leftover mashed potatoes! If you're preparing homemade Dutch oven mashed potatoes for a meal, make a little extra to speed up a shepherd's pie dinner later in the week.
Make sure you deglaze your pan after the meat is browned — this simply means adding some liquid and scraping the pan to loosen the bits of browned meat that stuck to the pan. This adds a ton of flavor to a dish! So when you add your broth in step 4, give the cast iron a good scrape.