Preheat the oven to 400 degrees. Line a baking sheet with parchment paper.
Whisk 1 egg until well beaten; set aside.
Thaw one sheet of puff pastry at room temperature for 20 minutes, or until you can unfold the pastry. Cut into 4 equal squares.
Place the sliced peaches in a bowl then sprinkle with sugar, cornstarch, and vanilla. Toss gently.
Layer three slices of peach over the center of each pastry square. Avoid getting the peach juice on pastry edges! Brush edges generously with beaten egg wash. Top each tartlet with a few raspberries and some sliced almonds.
Bake on the center rack for 15-17 minutes, or until puffed and golden at the edges, turning the baking sheet halfway through baking time. Side Note: Don't over-bake! They brown quickly towards the end. Remove from the oven and allow to cool on the pan for 10 minutes.
Make the glaze while the pastry cools, by combining the powdered sugar with the milk and vanilla. Whisk until creamy and smooth. Add more milk, if needed, to reach desired consistency.
Drizzle the glaze on top of the warm pastries. Serve and enjoy!