Preheat your oven to 180°C (350°F). Spread the bread cubes on a baking tray and toast for 10 minutes until lightly crisped. Set aside to cool while you prepare the rest of the ingredients.
In a large skillet, melt butter over medium heat. Add onion, celery, and garlic. Sauté for 5 to 7 minutes until vegetables are soft and fragrant. Stir in sage, thyme, salt, and pepper. Remove from heat and allow to cool slightly.
Place the toasted bread cubes in a large bowl. Pour the sautéed mixture over the bread. In a separate bowl, whisk together broth and beaten egg, then slowly add to the bread mixture, gently folding until the cubes are moistened but not soggy. Set aside.
In a small bowl, combine butter, olive oil, salt, pepper, thyme, sage, garlic powder, and onion powder. Rub this mixture all over the turkey breast, including under the skin where possible for deeper flavour.
If your turkey breast has a cavity, loosely fill it with quartered onion, apple, and celery. This will add moisture and aroma to the meat during roasting. Avoid overstuffing, as it can affect even cooking.
Place the seasoned turkey breast on a rack in a roasting pan. Add a bit of water or broth to the bottom of the pan to prevent burning and maintain moisture. Tent loosely with foil and place in the preheated oven.
Transfer the dressing mixture into a buttered baking dish. Cover with foil and bake alongside the turkey for 25 minutes. Uncover and bake for another 15 minutes until the top is golden and crisp.
Roast the turkey breast for 1½ to 2 hours, or until the internal temperature reaches 75°C (165°F) at the thickest part. Remove foil in the last 20 minutes to crisp the skin. Let rest for at least 15 minutes before carving.
While the turkey rests, arrange the baked dressing on a large platter. Carve the turkey into even slices and place them on top or alongside the dressing. Spoon any resting juices over the meat for added flavour.
Serve hot with classic sides such as cranberry sauce, gravy, or green beans. Garnish with fresh herbs like parsley or thyme for a finishing touch. This dish pairs well with both light and rich accompaniments depending on the occasion.