Begin by preheating the oven to 350° degrees F and spreading cubed sourdough in a single layer onto a baking sheet. Drizzle with olive oil and season with salt and pepper. Bake 15-20 minutes, until lightly toasted.
Set bread aside and increase oven heat to 375 degrees F.
Into a large skillet over medium heat, add butter. When butter is melted, add onion and celery. Saute 3 minutes, until softened. Add the chicken-style broth. Bring to a boil then reduce heat to low and simmer for 10 minutes.
Into a large mixing bowl, add mayonnaise, poultry seasoning, sage, and thyme. Stir to combine.
Add sourdough cubes to the mayonnaise mixture. Gently toss to coat the bread.
Gradually pour in broth mixture until all bread is soft.
Into a prepared 9"x9" glass casserole dish, add dressing mixture in an even layer.
Bake, uncovered, 30 minutes until top is lightly browned.