Preheat oven to 400 degrees. Coat a 13 x 9 inch baking dish with cooking spray.
Whisk the milk and eggs in a large bowl; stir in the muffin mix and let stand 2 minutes. Pour into the prepared baking dish and bake 20 minutes until a toothpick inserted in the center comes out clean. Cool and cut in ½-inch cubes. Allow to stand at room temperature 1 day or place on a baking sheet and toast in a 400 degree oven until golden.
Cook bacon in a large skillet: remove and transfer to a plate lined with paper towel. Crumble the bacon when cool.
Add the onion, carrot and celery to the drippings in the pan; cook, stirring occasionally, until the vegetables are somewhat softened, about 5 minutes. Stir in the cranberries and broth; cook 5 minutes.
Combine the cornbread cubes, crumbled bacon, vegetables, walnuts, thyme, sage salt and pepper in a large bowl. Transfer to the baking dish and bake 20 minutes, until thoroughly heated.