How to Make It
Preheat oven to 350°F. Grease 2 (13- x 9-inch) baking dishes with butter. Heat oil in a large skillet over medium-high. Add onions and celery, and cook, stirring occasionally, until softened but not browned, about 10 minutes. Add sage and garlic, and cook, stirring often, until fragrant, about 2 minutes.
Transfer cooked vegetables to a large bowl. Add cornbread, sandwich bread, parsley, salt, and pepper; stir until well combined. Gradually stir in stock until breads are evenly moistened. Scrape mixture into prepared baking dishes. Bake in preheated oven until hot and lightly browned, about 30 minutes.