Preheat the oven to 400 degrees F (200 degrees C). Cut the base off of the fennel bulbs, and cut a cone shape into the base to remove the core. You can see the core because it is whiter than the surrounding green. This is optional, but helps the fennel cook faster. Slice the fennel vertically (upright) into 1/4 inch thick slices.
Melt the butter in a large skillet over medium heat. Add the fennel, and fry for about 5 minutes. Stir in the half-and-half and creme fraiche until well blended. Transfer to a shallow baking dish. Sprinkle Parmesan cheese over the top.
Bake for 30 minutes in the preheated oven, or until the top is golden brown and the fennel is tender enough to pierce with a fork.