Preheat the oven to 350 degrees F and grease an 8x8 baking dish.
Heat the butter and olive oil in a frying pan over medium-high heat.
When butter is melted, add the onions and saute for 2-3 minutes. They will begin to soften and become translucent.
Add the minced garlic and saute for an additional 60 seconds.
Once the garlic is fragrant, add Italian seasoning, xanthan gum, chicken broth and heavy whipping cream. Mix well.
Cook the mixture down until it begins to thicken. This will be about 5 minutes.
Add in the mozzarella and parmesan cheese, and cook until the cheeses are melted and the sauce is thick. Stirring often.
Mix in the chicken and the palmini noodles.
Continue stirring and cooking for an additional 2 minutes.
Add mixture to a greased 8x8 casserole dish.
Bake uncovered for 30-35 minutes, or until the chicken tetrazzini begins to brown and bubble.