Melt the butter in a large enameled cast-iron pot or frying pan over medium-high heat. Add the onion and cook for about 10 minutes, until translucent and just starting to brown. Add the garlic and cook for 2 to 3 more minutes, until fragrant.
Add the ground beef, sage, rosemary, thyme, salt, pepper, and coriander and cook over medium heat, stirring regularly to break up the meat, until all of the moisture has evaporated and some pieces are starting to develop a deeper brown color. Add the tomato paste, broth, carrots, and peas, reserving ¼ cup of the peas for the topping. Stir to combine, then set aside.
Preheat the oven 300°F. If working in a frying pan, transfer the meat mixture to a 9 by 13-inch or similar-sized baking dish. Spread the cauliflower mash over the meat mixture. Sprinkle the top with the leftover peas.
Cover with a sheet of aluminum foil and bake for 30 minutes, or until the edges start to look bubbly. Remove the foil and return to the oven. Increase the oven temperature to 425°F and bake for an additional 10 to 12 minutes, until the cauliflower topping just starts to brown.
Let the pie rest for at least 15 minutes before serving. Garnish with the fresh parsley and serve warm.