Lay out bread and pretzels overnight to allow them to dry out. You read that right. That's the goal. You want them to be crisp to the touch.
Tear both loaves of bread into chunks, the pieces going into a large mixing bowl
Melt butter and saute garlic, onions, and celery together. To go the French Onion route, caramelize the onions, deglazing the pan with a big splash of beef broth.
Dump the contents of the plan over your breads, mix well till combined. (Pro-Tip, mix with your hands. Way faster)
Stuff into your bird, crockpot, or dutch oven and bake FOR THE ENTIRE TIME you cook yo' bird. (4ish hours @ 350.)