In a large pot, cover the potatoes with cold water. Bring to a boil and cook for 15 minutes. Add the cauliflower florets and boil another 5 minutes, or until the potatoes are soft. Drain, then mash with the milk. Stir in the blue cheese.

Meanwhile, add the onion to an ovenproof skillet set over medium heat. Sprinkle with salt; cook 3 minutes, until softened.

Add the carrots and celery; cook 3 minutes. Add the chicken and cook 5 minutes, or until cooked through. Stir in the flour.

Add the vegetable broth and hot sauce. Simmer 10 minutes, or until the sauce is thick. Remove from heat.

Use a spatula to spread the chicken mixture evenly in the pan. Top with the mashed potatoes.

Bake for 30 minutes, or until the potatoes begin to brown.