Ingredients: 2 tablespoons unsalted butter 1 large yellow or red onion, finely chopped Kosher salt and black pepper 3 celery stalks, chopped 8 garlic cloves, smashed and chopped 2 to 2 1/4 pounds boneless, skinless chicken thighs   1 cup chicken stock 1/2 cup white wine 1/2 lem…