Pour the milk and cream into a medium-sized saucepan.

Add the vanilla extract.

Warm the mixture until it just starts to simmer.

In a large bowl or jug, beat together the egg yolks and sugar, and then whisk in the flour.

Slowly pour the warm milk and cream mixture into the egg mixture (not the other way around or else you will have scrambled eggs), whisking as you do so until the custard is smooth.

Pour this mixture into a clean saucepan and whisk gently over medium heat until the custard thickens. This should take only a few minutes.

Continue whisking for another 1-2 minutes to allow the mixture to release a few bubbles.

Pour the custard into a bowl and set aside to cool.

I recommend covering the bowl with a layer of clingfilm pressed against the custard to stop a skin from forming.

Preheat the oven to 200°C (390°F) (without fan).

Line a baking tray with greaseproof paper.

Place the water, butter and salt in a large saucepan over medium-high heat until the butter has melted and the water just begins to boil.

Take the pan off the heat.

Add the flour.

Beat everything together with a wooden spoon until the mixture comes together in a dough and comes away from the sides of the pan.

Tip the dough into the bowl of an electric stand mixer.

Using the flat paddle attachment, beat the mixture for a few seconds to knock out the air and to cool the dough a little.

Crack the eggs into a small bowl and, with the mixer on, add one egg at a time and beat until the mixture is thick and smooth. The consistency should be such that it should hold its shape once piped into a ball.

Fit a 2 cm (1 inch) plain nozzle into a piping bag and pipe little rounds onto the baking tray about 5 cm apart.

Fill a small cup with water to use to wet your fingertips and press down any pointy tips on the rounds of dough.

Bake for about 20-25 minutes until it is a pale, golden colour.

To check if the choux pastry buns are cooked, they should sound hollow when tapped on the bottom.

Remove to a cooling rack and pierce the underside of each choux pastry bun with a pin or cake skewer to let the steam out and to prevent them from becoming soggy.

Simply melt the cream and chocolate together in a saucepan over medium heat.

Whisk the mixture together until it is thick and smooth.

The chocolate sauce should be served warm.

The sauce will thicken as it cools but it reheats easily.

If the sauce separates upon reheating, give it a good whisk.

Fit a piping bag with a small plain nozzle and fill it with the custard.

If there are no openings at both ends of the choux pastry buns, simply use the tip of a small knife or chopstick to create an opening large enough for the nozzle.

Fill the choux pastry buns by inserting the nozzle into the openings. If you are making large éclairs, it is best to fill them with a bit of custard from both ends. If you are making small éclairs, it is usually fine to fill them from just one end.

The choux pastry buns are quite hollow inside and will fill easily with the custard, but be careful not to overfill them.

Dip the top of each éclair into the chocolate ganache to coat and allow to set.