Begin by cubing about 6 cups of stale bread into roughly 1-inch pieces. Dice apples into similar-sized chunks for even distribution throughout the pudding.
In a large mixing bowl, whisk together 4 cups milk, 1 cup granulated sugar, 4 large eggs, 2 teaspoons vanilla extract, and 2 teaspoons ground cinnamon until well combined.
Grease your baking dish with 1 tablespoon unsalted butter. Add the cubed bread and diced apples into the custard mixture, folding gently to coat evenly. If using turkey bacon, fold in cooked and crumbled 1/2 cup now. Let sit for 10-15 minutes to absorb custard.
Pour half of the bread pudding mixture into the baking dish. Drizzle half of the caramel sauce over the top, then add the remaining bread pudding mixture. Finish with the rest of the caramel sauce drizzled on top.
Preheat oven to 350°F (175°C). Bake uncovered for 50-60 minutes until the top is golden brown and a knife inserted comes out clean.
While pudding cools slightly, whisk together 1 cup powdered sugar, 2 tablespoons milk, and 1/2 teaspoon ground cinnamon until smooth to make the cinnamon glaze.
Once slightly cooled but still warm, drizzle the cinnamon glaze over the top. Serve immediately for best texture and flavor.