For the chocolate custard:

1. First, melt the chocolate over a bain-marie (water bath). To do this fill a saucepan with 5cm (2 in) of water and place over low-medium heat. Place the chopped chocolate into a smaller saucepan. Place this pan on top of the first pan.
2. Melt the chocolate, stirring with a spatula from time to time. Take the pan off the heat as soon as the chocolate is smooth and has completely melted. Set the pan aside and let the chocolate cool down to room temperature.
3. Pour the milk and cream into a heavy-based saucepan and place over medium heat. Bring to just below a boil, stirring frequently with a wooden spoon, then take off the heat.
4. In a mixing bowl whisk the egg yolks and cornflour together for 1min30. Check the temperature of the chocolate and milk with a thermometer (or dip a finger) to make sure they have cooled down to around 43°C (110°F). If they are too warm, the egg yolks will cook and scramble.
5. Incorporate half of the melted chocolate, followed by half of the milk mixture. Mix until fully incorporated then repeat with the other half of the chocolate and then the remaining milk. I find it easier to use a spatula and an up and down motion.
6. Pour the mixture back into the saucepan and place over medium heat. Stir constantly with the whisk, scraping the bottom of the pan as you stir. If it gets too hot, the custard will curdle.
7. Cook and stir until the chocolate custard has thickened nicely, about 6 min. The custard should be glossy, coat the back of a spoon and be almost as thick as pastry cream.
8. Tip the chocolate custard into 3 ramekins or small serving bowls with a 200ml capacity.  If you want to prevent a skin from forming on top of the custards, cover them with plastic wrap, pressing it directly onto the surface of the custards.
9. Let the chocolate custards stand until they reach room temperature then place them in the refrigerator for at least 4h.

For the whipped cream (crème chantilly):

1. Place the whisk and the mixing bowl in which you will whip the cream for 15 min in the freezer.
2. Take out the whisk and bowl from the freezer and the cream from the fridge. Whip the cream with a hand mixer on medium speed until you reach the soft peaks stage.
3. Add the extract, sugar and stabilizer (if using). Increase the speed and mix until everything is incorporated and the cream thickens. Lift up the beaters of your hand mixer, the peaks should be stiff and stand straight up.
4. Taste and adjust the sweetness according to your preferences.
5. Spoon the cream on top of custards. For a neater result; put the whipped cream into a piping bag with your preferred star-shaped nozzle and twist the bag. Pipe away and serve immediately.