These are all vegan do-able. Try a sauce chocolat by melting four ounces of semisweet or bittersweet chocolate with 4 ounces of water and allowing it to cook until a sauce texture is achieved. You must know your ingredients, how they interact and how they cook. The finesse of the chef is what has people coming back for more. A truly talented French chef can throw some fresh vegetables into a pan with some herbs and a little wine, serve that over some sliced potatoes and make a dish fit for a king.
French cuisine is, of course, regional.
Some of the regions lean more to using a lot of fat in their dishes, but just as many use little fat and accent grains, veggies, breads and small portions. Cook for maximum flavor, using the freshest high quality ingredients you can find. Make some for now and some for freezing. In a medium saucepan, heat oil. Add onion and saute until soft.