Step 1: Make the Vanilla Cream. Heat milk with the sugar in a small saucepan, stirring until the sugar dissolves and the milk is hot but not boiling. In a bowl, whisk together the egg yolks, cornstarch, and vanilla extract until smooth. Slowly pour about 1/3 of the hot milk into the egg mixture while whisking to temper the eggs.

Pour the mixture back into the saucepan with the remaining milk. Cook over medium heat, stirring constantly, until the cream thickens, about 2-3 minutes.

Remove from heat and stir in butter. Transfer the cream to a bowl (or let it cool slightly in the saucepan) and cover with plastic wrap, pressing it directly onto the surface to prevent a skin from forming. Refrigerate while preparing the pastry. 

Step 2: Preheat the Oven. Preheat the oven to 350°F (180°C). Line a baking sheet with parchment paper. 

Step 3: Cut the Dough. Cut the puff pastry sheet into 6 equal squares. 

Step 4: Shape the Flowers. Take one square and fold all four corners toward the center. Flip it over. Fold the four new corners toward the center again and gently press the middle with your finger. Flip the pastry once more. Carefully unfold only the top layer of corners to create a layered flower shape. Flip it over. 

Step 5: Bake. Place the shaped flower bases on the prepared baking sheet.

Beat egg with a fork and brush the tops.

Bake for 18-20 minutes, until puffed and golden brown. 

Step 6: Fill and Serve. Let the pastries cool slightly. Place a zip-lock bag in a glass with the edges folded over the rim, fill it with cream, cut off a corner, and pipe some vanilla cream into the center of each flower, top with a fresh raspberry, and dust with powdered sugar before serving.