Preheat your oven to 400 F/200 C. Peel, wash, and thinly slice the turnips into 1/8 inch slices. Transfer to a pot and cover with hot water.
Step 2
Place the pot over high heat and bring to a boil. Drop the heat to medium-low and let it simmer for 10 minutes until softened. Drain the turnip slices and set aside.
Step 3
Pour the heavy cream into a saucepan and place over medium heat. Whisk in the xanthan gum, garlic powder, salt, and pepper until they dissolve. Bring to a simmer then take off the heat. Taste and adjust seasoning if needed.
Step 4
Lightly grease the casserole dish and spread 2 tbsp of white sauce at the bottom. Add one layer of turnips and top with ½ cup cream sauce. Spread and sprinkle ¼ cup mozzarella and 2 tbsp cheddar cheese on top.
Step 5
Repeat until you have a total of 3 layers, ending with white sauce and cheese. Bake for 25-30 minutes or until the turnips are fork-tender and the cheese is golden. If the top starts browning fast, cover with aluminum foil.
Step 6
Garnish with chopped parsley. Cut into 4-6 slices. Serve immediately.