Set oven to 400F Peel and very thinly slice the onion. I used the 1/8 inch setting on my mandoline, but you can use a knife if you like, just get the slices as thin as possible. Break apart the rings and pile the onions right into the frozen (not thawed) crust. Even them out from side to side. you may not need the entire onion if yours is large. Whisk the eggs and cream together, making sure to break up the eggs completely. Stir in the herbs, mustard, and Parmesan. Add salt and pepper. Scatter the shredded cheese on top of the onions, and then crumble the goat cheese over that. Pour the egg mixture over all. Spread out the herbs, if necessary, across the surface of the quiche (they can tend to clump toward the center after you add the liquid.) Bake for about 50 minutes, give or take, until the quiche is puffed, browned, and set in the center.