Preheat oven to 200C.
Bring a pot of salted water to boil, add cauliflower & garlic to cook for 12 minutes until fork tender.
Drain, then season with salt and black pepper.
With an immersion blender, blend cauliflower until smooth and creamy.
Heat oil in pan, and saute potatoes, onion, celery, carrot, and mushrooms until soften. About 8 minutes.
Then add minced garlic, meat, and Italian seasoning to cook until beef is brown.
Stir in tomato paste until combined.
Add arrowroot flour to chicken broth and whisk until combined.
Then slowly add to meat mixture, stirring consistently.
Allow to cook until thickened. Season with salt and black pepper.
Transfer filling to casserole dish, then top with cauliflower mash.
Bake for 30 minutes until bubbly.