Preheat the oven to 400°F.
Heat the olive oil or butter in a large skillet or Dutch oven over medium heat.
Add the diced onion and sauté for 5–7 minutes, or until translucent.
Add the ground beef and cook until mostly browned and cooked through.
Stir in the minced garlic and cook for 1 minute.
Add the Worcestershire sauce, tomato paste, dried parsley, rosemary, thyme, salt, and black pepper. Cook for 1–2 minutes, stirring to combine.
Sprinkle the gluten-free flour over the beef mixture and stir until evenly incorporated with no visible clumps.
Pour in the beef broth and add the corn, peas, and carrots.
Reduce the heat to low and simmer for about 10 minutes, stirring occasionally, until the filling thickens and the flavors blend.
Transfer the filling to a 9×9-inch casserole dish or a similarly sized baking dish.
Spread the mashed potatoes evenly over the beef filling.
Use a fork to gently fluff the potato surface. This creates little ridges that become golden and lightly crisp during baking.
Bake for 20–25 minutes, or until the potato topping is lightly golden brown.
Remove from the oven and let the Gluten Free Shepherd’s Pie cool for about 10 minutes.
Garnish with chopped chives or fresh parsley before serving.