Saute the chopped onion in a little butter until it is lightly golden. Set aside.
Cut the meat into strips and set aside.
In the meat grinder, grind the meats (hare and sausage meat), onion, garlic, and parsley, alternating them.
Put the mixture in a large bowl.
Add salt, pepper to taste, thyme (to taste), and Cognac.
Mix well with your hands.
Put the preparation in a terrine, doming the meat on top.
Place a few bay leaves and a few thyme sprigs on top.
Cover with a lid and bake in a preheated oven at 350 F (180 C) for 1 hour, then remove the lid and continue cooking for another 30 minutes.
Remove from the oven and let cool completely on the counter before refrigerating.
A jelly will have formed at the bottom of the terrine.
If you want to make it ahead and freeze it, you can cut thick slices and wrap them in aluminum foil, then in a freezer bag.