Preheat oven to 300°F (150°C). Spread out the challah on a baking sheet and bake for 25 minutes. Set aside to cool.

Heat the olive oil in a medium-sized pot and add the onion, garlic, celery, and carrot. Sauté until soft and deeply caramelized, about 10 minutes. Add the chestnuts, turkey, sage, thyme, and stock and bring to a boil. Taste and adjust seasoning, adding salt (if needed), and pepper.

Place the challah into a large mixing bowl and pour the stock and vegetables over it. Stir until the ingredients are well incorporated. Cool the mixture for a few minutes and then mix in the eggs. Pour the stuffing into a greased 9×13-inch (20×30-cm) baking pan and bake at 350°F (180°C) for 30–45 minutes, until stuffing is golden brown.