Peel then cut the rutabaga and turnip into thin slices.
Put the slices in a pot of boiling water for 3 minutes, drain, rinse with cold water and let hang out.
Chop the herbs bring a cup and a half of heavy cream with the herbs, chopped garlic and salt and pepper to a boil, then let simmer for about 4 minutes.
Pour a little bit of the cream in the casserole dish, just to cover the bottom. make a layer of rutabaga/turnip, add grated Gruyere and Parmesan. pour some more of the heavy cream mix, add another layer of rutabaga/turnips and cheese and so on and so forth until you are running out of rutabaga/turnips. the final layer should just be the veggies with the grated cheese liberally on top. i sprinkled each layer with salt and pepper as i was putting it together.
bake for 40-45 minutes, until the top layer is golden brown and crispy and you know, it just *looks* don.