Chocolate Pastry Cream

Prepare a large bowl of ice water (enough to put a pot in). Set aside.

Combine 40 grams of sugar with the egg yolks in a large bowl. Whisk immediately with a wire whisk until the mixture is pale and smooth. Sift in the flour and whisk till smooth. Set aside.

Combine the milk, butter and the remaining 10 grams of sugar in a medium pot and warm over medium heat until it comes to a boil. Remove from heat.

Pour the hot milk, little by little, bit by bit, into the egg yolks, whisking constantly until 1/4 of the hot milk has been added. (Don't add the hot milk too fast, otherwise it'll scramble the eggs and you'll have to start over.)

After 1/4 of the hot milk has been added, add the hot milk in a slow and steady stream, whisking constantly - until 1/4 of hot milk is left. This whole process is called tempering.

Once the egg yolks have been tempered, pour the egg yolk mixture back into the pot and whisk to mix them altogether. Place the pot back on medium heat and with a wooden spoon, stir the mixture constantly until the mixture has thickened and has started to boil - you'll see huge air bubbles popping out of the custard - that's a sign that the pastry cream is ready.

Remove the pot from heat and place it in the bowl of ice water. Stir the pastry cream constantly until it has cooled down. Stir in the vanilla paste / extract and whisk in the cooled melted chocolate.

If using immediately, spoon the pastry cream into a piping bag and keep it refrigerated until needed. If not, transfer the pastry cream into a container, place a plastic wrap (cling film) directly onto the surface of the pastry cream (to prevent a skin from forming) and refrigerate for up to 3 days.