Thaw frozen puff pastry for 3-4 hours in the refrigerator. Unroll it and place onto a baking sheet that is lined with parchment paper. Pre-heat oven to 400 F. Score the pastry to make about an inch of border on the sides. Use a knife to lightly make the mark without cutting the pastry all the way.
In a medium bowl, combine peaches, flour, cinnamon, and sugar. Mix to incorporate. Arrange the peaches over the puff pastry, making sure to leave the outside borders clean. Sprinkle sliced almonds on top. Brush the edges with the beaten egg.
Combine powdered sugar, vanilla and milk. Stir until smooth.
Adapted from Natasha's Kitchen