Preheat oven to 350°F. Tear white bread into bite-sized pieces.

Chop celery and onion into small chunks. Brown ground beef and sausage in a skillet, breaking into pieces. Drain excess fat. In the same pan, sauté celery and onion until softened.

In a large bowl, combine bread pieces, browned meats, and sautéed vegetables. In a separate bowl, whisk egg and milk together, then pour over stuffing mixture. Gently fold until bread is evenly moistened. Season with sage, salt, and pepper.

Transfer mixture to a casserole dish. Bake for 45-50 minutes until top is golden brown and crispy. Alternatively, stuff turkey, ensuring both reach safe temperatures.