Bring a large pot of water to a boil. Once water is boiling, add large pumpkin chunks and potatoes. Boil for 10-15 minutes or until pieces can be pierced easily with a fork. Strain out water and let cool slightly while you prepare the filling.
Melt 2 tablespoons of butter in a large cast iron skillet over medium heat. Add onions, garlic and small cubed pumpkin and saute until onions are translucent and fragrant, 5-10 minutes. Add beef, brown slightly, and then toss in fresh herbs.
Add flour, beef stock and frozen peas and stir to combine. Let cook over medium heat, stirring occasionally, until beef is no longer bright pink.
While beef mixture is cooking, mash your pumpkin and potatoes. Add 4 tablespoons of butter and heavy cream to the pot where the pumpkin and potatoes have been cooling. Using a hand mixer or immersion blender, cream everything together until smooth. Season with salt and pepper to taste.
Once beef mixture is cooked, taste and season with salt and pepper as necessary. Turn off the burner your cast iron skillet has been cooking over and preheat your oven’s broiler (on high.)
Spread the mashed pumpkin and potato mixture evenly over the beef in the cast iron skillet. Top with grated Parmesan and place under the broiler until the top has a lovely golden hue, which can take anywhere from 5-15 minutes. Just keep a close eye on it as it is under the broiler as things can take a turn towards burnt very easily!
Serve pie by scooping the mixture out into bowls while it’s still warm.