In a large saucepan, whisk the custard powder and the sugar until combined. Pour in around half of the milk and whisk until smooth. Add the rest of the milk and mix well.

Over medium-high heat, cook the mixture while whisking constantly. The mixture should thicken up a lot.

Remove the custard mixture from the heat and stir in the butter and vanilla until smooth. Cool slightly and transfer to a heat-proof container or bowl. Chill in the refrigerator for at least 2 hours to overnight. The mixture will firm up significantly - whisk or blend the custard until it's runny and smooth again.

Preheat oven to 200°C (390°F) and line 1-2 baking trays with parchment paper.

Lightly brush one sheet of puff pastry with maple syrup and place the other sheet on top. Cut the pastry into squares (or rectangles) with a sharp knife or pastry cutter.

Arrange the pastry squares on your baking trays. Using a small knife, gently score a smaller square inside each square to form a border. Brush the tops with maple syrup.

Bake the puff pastry squares for 15-20 minutes or until puffed and golden. Cool completely.

Use a small serrated knife to cut along the scored lines and press down the pastry in the middle.

Dollop 1-2 teaspoons of jam in the middle of each pastry and spread to fill the middle. Use a piping bag or small spoon to fill each pastry with the cooled custard. Top with fresh berries, a dusting of powdered sugar and sprinkle with rose petals. Enjoy!