Preheat your oven to 350 degrees.
Let's start by making the cauliflower mash! Place a couple inches of water in a pot, and bring to a boil over high heat. Once the water is boiling, place a steamer insert into the pan and add the cauliflower florets. Cover the pan and allow it to steam until the cauliflower is soft and easily pierced with a fork.
Drain the water out of the pan and add the cauliflower. Turn the stove back on to medium heat and allow any extra water to evaporate out of the pot. This is the key to a fluffy mash! Add the ghee/butter to the pot, and blend with an immersion blender until smooth**. Add salt to taste. Set aside while you make the casserole base. **Another option is to place the cauliflower in your food processor or blender and process/blend until smooth.
Now let's make the base for the casserole! Melt the ghee in a large pan over medium heat. Add the onion and celery to the pan and sauté until tender, about 5 minutes. Add the garlic to the pan and sauté until fragrant, about 30 seconds. Add the broccoli to the pan and stir well. Turn off the heat.
Add the turkey, mayonnaise, eggs, poultry seasoning, onion powder, dried sage, garlic powder, sea salt & black pepper to the pan. Stir the mixture really well.
Pour the turkey mixture into a 9"x 9" dish, using a spatula to smooth the top. Scoop the cauliflower mash on top of the turkey mixture in the dish, using a spatula to smooth the top of the casserole. Bake uncovered for 45 minutes-1 hour, or until the top of the casserole begins to lightly brown. Let stand for 5 minutes before serving. Enjoy!