1: Start by heating your milk, cream and vanilla in a saucepan just until hot to the touch. Set aside.
2: Whisk your yolks in a bowl, sugar and cornstarch until thick. Add hot milk mixture slowly while whisking.
3: Return mixture to saucepan at medium heat and whisk often, until mixture becomes custard like. Transfer to bowl, mix butter in. It will melt in the mixture.
4: Cover with plastic wrap directly on custard and place in the fridge until cold, about 2 hours.
5: Preheat oven to 350 F. Line a baking sheet with parchment paper.
6: Place puff pastry on it. Place a dollop of about 1.5 tbsp of custard on puff pastry and repeat each with about 1/2 inch in between each.
7: Add half apricots face down on each dollop of custard. Slice pastry in between apricots to form your squares.
8: Brush egg wash on pastry only, sprinkle sugar and cinnamon.
9: Bake for 45-50 minutes, or until golden.
10: Once cool, sprinkle powdered sugar on top.
