Add both the biscuit pieces and the bread cubes to a large rimmed baking sheet- spread out in an even layer.
8 cups chopped cheddar bay biscuits, 6 cups cubed white bread
Bake at 300° for 25-30 minutes, stirring occasionally, until they're dried out. Then let the bread crumbs cool completely.
Add the butter to a medium skillet set over medium heat. Add the onion, celery, and carrots- stirring together and sauteing until softened. Stir in the herbs, salt, and pepper, and stir to evenly combine. Set aside and let cool.
1 cup butter, 2 cups diced yellow onion, 1 cup diced celery, 1/2 cup diced carrots, 1 tsp dried sage, 1/2 tsp dried thyme, scant tbsp dried rosemary, salt & pepper
Add the bread and biscuit pieces to a large mixing bowl and gently toss to combine. Add the broth to the bowl and stir until evenly combined while it soaks it up.
3 3/4 cups chicken broth
Transfer the mixture to a greased 9x13" casserole dish and spread it out in an even layer.
Bake at 350° for 25-30 minutes, until set and golden brown on top.