Preheat oven to 350 degrees.

In a large combine milk, cream, and vanilla. Add in cubed bread and gently combine until coated. Let sit at room temperature.

In a 12 inch cast iron skillet, melt butter over medium heat. Whisk in brown sugar and white sugar until combined. Remove from heat.

Whisk in eggs (you can temper in a little of the butter mixture first) and 4 tbsp bourbon until combined. Add in apples, cinnamon, and 1/2 cup pecans, and stir.

Pour in bread mixture and fold in until combined.

Sprinkle on remaining 1/4 cup pecans and turbinado sugar. Cover with lid or foil.

Bake for 55 minutes. Uncover and bake until golden brown about 15 minutes. Inserting a wooden pick or cake tester in the center and be sure it comes out clean. 

In a small bowl, whisk together powdered sugar, melted butter, 2 tbsp bourbon until smooth. Whisk in heavy cream until smooth. Drizzle sauce on top of warm bread pudding and serve immediately while warm.