Start with the crust. In a large bowl mix the flour, sugar and salt.
Add the cold cubes of butter. Press the butter into the flour with your fingertips until you have pieces of butter that are pea-sized and the mixture resembles wet sand. You can also cut the butter into the flour using a pastry cutter or a fork.
Add the ice water 1 tablespoon at a time. Lightly toss the dough to incorporate the water. After adding 6 tablespoons of water, the dough should be in larger clumps.
Transfer the dough onto a piece of plastic wrap or a large ziploc bag. Press the dough together and form into a disk. Wrap tightly and refrigerate.
In the meantime make the pastry cream. In a large bowl, whisk together the sugar and eggs until smooth. Whisk in the cornstarch. Set aside.
In a pot over medium heat warm the milk, lemon zest and vanilla until you see wisps of smoke (right before the milk begins to boil). Turn off the heat.
Temper the eggs. Pour a very small amount of milk at a time into the egg mixture, whisking in between each addition.
Once all the milk has been added, return the mixture to the pot over low to medium heat. Stir constantly until thick and creamy, until it just reaches a simmer.
Pour the cream into a clean bowl. Cover with plastic wrap, with the wrap touching the top layer of the cream so a skin does not form. Let cool and then refrigerate to cool completely.
Preheat oven to 350°F (180°C).
On a floured surface, roll out the dough to ¼ inch thick. You may need to let it sit out at room temperature for a couple minutes to be able to roll it.
Cut out 6 inch circles. Place each one in a tart shell, ensuring the dough is pressed into each shell. Trim off any excess dough.
Line each shell with a square of parchment paper. Fill them with pie weights (or uncooked rice or beans). This will prevent the dough from puffing up in the oven.
Place each tart on a larger baking sheet and bake for 15 minutes. Carefully remove the pie weights and place them back in the oven for 5 minutes.
Once completely cooled, pipe pastry cream into each tart and arrange any berries/fruit on top. Dust with icing sugar just before serving.