Preheat the oven to 400°F (200°C).

Steam the cauliflower florets in a steamer basket over boiling water for 12 minutes until fork-tender. Drain thoroughly and pat dry with a clean towel to remove all excess moisture.

While cauliflower is steaming, place a large skillet over medium-high heat. Add the ground beef and brown until no longer pink, approximately 7 minutes. Drain 75% of the rendered fat.

Add the diced onion, minced garlic, and chopped mushrooms to the skillet. Sauté for 6 minutes until onions are translucent and mushrooms have released their moisture.

Incorporate the tomato paste, thyme, rosemary, salt, and pepper into the meat mixture. Cook for 2 minutes to caramelize the paste.

Pour in the beef broth and Worcestershire sauce. Simmer uncovered for 8-10 minutes over medium heat until the liquid has reduced by half and the mixture is thick.

Prepare the topping: Place the steamed cauliflower into a food processor with the butter, cream cheese, and 1/2 cup of the shredded cheddar. Process until completely smooth and velvety.

Transfer the beef mixture into a 9x9 inch (23x23 cm) ceramic baking dish, spreading it into an even layer.

Spoon the cauliflower mash over the beef and spread to the edges using a spatula. Use a fork to create decorative ridges on the surface.

Sprinkle the remaining 1 cup of shredded cheddar cheese evenly over the cauliflower mash.

Bake for 20-25 minutes until the cheese is bubbling and the peaks of the mash are golden brown.

Remove from the oven and allow the pie to rest for 10 minutes to set before serving.