In a medium saucepan, combine 1 cup of milk, 1/2 cup of heavy cream, 1/2 cup of sugar, and 2 tablespoons of corn starch over low heat. Whisk continuously until the mixture begins to simmer and thickens slightly, about 5 minutes.

Remove from heat and let it cool for about 5 minutes.

In a separate bowl, crack 6 egg yolks and add 1 teaspoon of vanilla extract. While whisking, slowly pour the warm cream mixture into the egg yolks.

Strain the combined mixture through a fine mesh sieve into another bowl.

Preheat your oven to 475°F (245°C). Roll out thawed puff pastry sheets and cut out 3-inch circles for the tartlet baking tray.

Press the pastry circles into the molds without air bubbles.

Fill each pastry shell with custard, about ¾ full. Bake for 15-20 minutes, monitoring for golden brown spots.

Once baked, cool in the tray for about 10 minutes, then transfer to a wire rack.

Serve warm or at room temperature, optionally dusted with powdered sugar.