Indeed many of the top restaurants will be closed in the mid-December period, especially in the countryside. Besides, the countryside in mid-December is quite triste. In addition, you want creative cuisine with a new chef, plus lodging for this difficult pperiod. I wonder if you could prioritize your conditions. As is, the choice is not large. Example: Ferme de la Ruchotte. If it is open, then you get your creative chef in the Burgundy countryside, but the winterscape is bleak (everywhere in Burgundy, not just there), and it has no lodging sur place.
Olhabidea in Sare, in the Basque country, has a creative chef, and upstairs are 4 lovely rooms, but it is usulaly closed for several winter months. Worth looking up.
Ditto Mas de la Madeleine on the hills of the lovely Medieval town of Largentière in the Ardèche. Same problem as Olhabidéa. But worth it to contact those places to see if they are open in the dead of winter.
The food in both Olhabidéa and Mas de la Madeleine is insanely good and creative, and a large part of the ingredients come from their potager.
As for Ferme de la Ruchotte, the chef used to work for starred restaurants and preferred to grow his own ingredients and raise his own rare breeds of poultry, a factor that he thinks the Michelin people care less than whether the restroom has marble. He is not wrong. And when you go to eat there, you track mud into the his restaurant because, duh, it's a farm. That guarantees to freak out the Michelin guys.
My general bet for a location with a wider hcoice of restaurants and lodging would be the Provence town of Arles. Not exactly the countryside with fields - bald at that period, - but nearly. it is a beautiful small town with a concentration of very good eateries, from starred temples like Rabanel and La Chassagnette to delicious pizzeria takeouts.
Another choice of mine would be Ciboure on the Atlantic coast on the Spanish border. The beautiful village is a listed Plus Beau Village de France and is adjacent - within walking distance - to St Jean de Luz. Like Arles, it has a wide range of restaurant choice, from starred places to casual pinxos bars. My go-to table in Ciboure would be Chez Mattin (pronounced Maatcheen), excellent and very festive, but it's classical Basque cusine with seafood focus and you don't want classic, right ? Actually San Sebastian is just on the Spanish side, a 40-minute drive away. It my be my favoriate food city of Europe. A Birthday Pinxos Crawl may not be a birthday thing but it's creative and outrageously good.
Hope this helps.
