Roll the puff pastry into a large rectangle roughly the size of the baking sheet pan. Place into the refrigerator until ready to use.
Slice the peach halves into eighths.
In a large bowl combine the brown sugar, bourbon, cinnamon, cornstarch, and nutmeg and mix evenly. Toss the peaches in the sugar mixture gently until evenly coated.
Remove the puff pastry from the refrigerator and pour the peach mixture into a line in the center of the puff pastry in the direction of the longest side. Cut long strips about an inch thick on each side of the line of peaches. Starting from the top fold the top edge over the end of the peach mixture. Alternating sides overlap each of the strips in a braid-like fashion.
Mix the egg and milk together. Brush the egg wash mixture over the top of the strudel. Sprinkle the turbinado sugar on top.
Bake for 35-45 minutes until golden brown. Allow to cool before slicing.