To make the custard cream

1. Warm up the milk until hot, but not boiling. In a medium size pan, add the egg yolks, sugar, and the cornstarch. Whisk well until smooth and fluffy. Add the milk a bit at a time, while whisking well so no lumps form.
2. Place the pan over medium heat and stir continuously until it reaches a slow boil. The cream will thicken, so be careful not to let it stick to the bottom. Lower the flame and cook for a couple of more minutes, until you reach the desired thickness. Pour the cream into a glass bowl or piping bag, and let it cool down. Refrigerate for at least half an hour or until ready to serve.

To make the tartlets

1. In a large bowl beat the egg with the sugar until light and fluffy. Add the cubed softened butter, and beat some more. Add the vanilla extract, salt, and flour and blend until the dough comes together. Wrap into plastic wrap, make into a disc, and refrigerate for 30 minutes or longer.
2. Preheat the oven to 350° F (175° C). Grease the tartlet mold with butter and flour (or spray). On a lightly floured surface, roll the dough making sure it doesn't stick to the counter. Cut with a round cookie cutter (3 inches (7.5 cm) in diameter). Place them into the mold, pressing down the middle gently with your fingers. Prick the bottom with a fork. Bake the empty shells for about 14-15 minutes, in the middle of the oven, until just golden at the edges. Let cool down completely.
3. When ready to serve, pipe some of the custard cream into the tartlet shells and top with fresh berries.
   

Best if filled with cream and topped with fruit before serving. Store the cream or filled tartlets in the refrigerator