In a large mixing bowl (or the bowl of a standing mixer) add the flour, sugar and baking powder. Mix well.

Add the butter and mix again, incorporating until you have a sand-like mixture. Then add the eggs and mix to form a proper dough, adding, if need be, add a spoonful or two of milk or water.

Wrap the dough and plastic wrap (cling film) and let it sit in the refrigerator for at least 30 minutes.

In a standing mixer bowl, whisk together the egg yolks and sugar until smooth and the mixture forms ‘ribbons’ as the whisk rotates.

Add the flour or cornstarch slowly, bit by bit, into the mixture until fully incorporated. The mixture should be a pale yellow and quite fluffy.

Meanwhile, heat the milk (or milk and cream) over moderate heat until hot but not boiling. You will see little bubbles just beginning to form around the edge of the pot. (If you are using a vanilla bean, add it to the milk and let it steep for a few minutes, then remove it.) Take the milk off the heat and whisk it, little by little, into the mixer bowl.

Now pour the whole mixture from the bowl into the pot (along with the vanilla extract if using) and place it over very gentle heat, whisking continuously and vigorously. After a while, it should begin to thicken. Keep stirring until you have a thick custard that pulls away from the bottom of the pot as you whisk.

Remove from the heat, stir in the grated lemon zest if using, and let the mixture cool. It will thicken further as it cools. If keeping for longer than 30 minutes or so, cover with film wrap to avoid a film forming on top.

Take the dough and roll it out into a round a bit wider than the tart plate you're using. (The dough should cover the bottoms and sides.)

Lay this round onto a well buttered 20cm (8 inch?) tart dish, making sure to cover the bottom and sides. Trim off any excess. Puncture the bottom here and there with a prongs of a fork.

Cover the dough with a round of parchment paper, add pie weights (or just some old dried beans) on top to weigh it down.

Remove from the oven and let the baked crust cool completely. (Remove the parchment paper and weights/beans when they're cool enough to handle safely.)

With the help of a spatula, pour the pastry cream into the tart dish and smooth out as evenly as possible across the bottom of the crust.

Now take the berries and arrange them on top of the pastry cream, if you like in a decorative pattern or just willy-nilly. Most berries should be left whole. But, unless they're very small, strawberries are best cut in half or even quarters, depending on their size.

If desired, dust the berries with confectioner's sugar, or serve as is.