Preheat oven to 400 F. In a medium bowl, whisk together flour, cornmeal, sugar, salt and baking powder. In a measuring cup, whisk together milk and vinegar.
Pour milk mixture, egg and vegetable oil into the dry ingredients. Whisk until smooth. Pour cornbread mixture into a lightly greased 9-inch round baking dish. Bake for 20-25 minutes. Let cool slightly and crumble cornbread into a large bowl.
In a large skillet over medium heat, melt butter cook onion and celery until softened. Mix with crumbled cornbread, vegetable broth and poultry seasoning. Form mixture into small balls and place onto a large greased baking sheet. Bake for 15-20 minutes.
