01 - Preheat oven to 400°F.
02 - Steam or boil the cauliflower florets until very tender, about 10-12 minutes. Drain well and set aside.
03 - Heat olive oil in a large skillet over medium heat. Add onion, garlic, carrots, and celery. Sauté for 5 minutes until softened.
04 - Add ground beef. Cook, breaking up with a spoon, until browned and cooked through. Drain excess fat if needed.
05 - Stir in tomato paste, thyme, rosemary, and smoked paprika. Cook for 2 minutes.
06 - Add beef broth and Worcestershire sauce. Simmer uncovered for 10 minutes, until slightly thickened. Stir in peas. Season with salt and pepper. Remove from heat.
07 - Combine cooked cauliflower, butter, milk, and Parmesan in a food processor or with a hand blender. Puree until smooth and creamy. Season with salt and pepper.
08 - Spread the beef mixture evenly in a 9x13-inch baking dish. Top with cauliflower mash, smoothing over the surface.
09 - Bake for 20-25 minutes, until the top is slightly golden and filling is bubbling.
10 - Let rest for 10 minutes before serving.