01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners or grease thoroughly.
02 - Whisk together whole milk, heavy cream, eggs, granulated sugar, brown sugar, vanilla extract, and salt in a large bowl until fully combined.
03 - Add bread cubes to the custard mixture, ensuring all pieces are coated. Allow to soak for 10 minutes.
04 - Combine diced apples with lemon juice and cinnamon in a separate bowl.
05 - Gently fold the apple mixture and half of the caramel sauce into the soaked bread. If desired, fold in chopped nuts.
06 - Divide the prepared mixture evenly among the muffin cups, filling each to the top. Drizzle remaining caramel sauce over each muffin.
07 - In a small bowl, stir together topping brown sugar and cinnamon. Sprinkle evenly over the filled cups.
08 - Bake for 28 to 32 minutes, until muffins are golden brown and centers are set.
09 - Allow muffins to cool in the tin for 10 minutes, then transfer to a wire rack. Drizzle with extra caramel sauce before serving, if desired.