method
1. Whisk the egg yolks, cornstarch and superfine sugar in a bowl.
2. Heat the milk until it is hot but not boiling, and whisk it into the egg yolk mixture. Place the bowl over a saucepan of gently simmering water and stir continuously with a wooden spoon for about 20 minutes, or until the custard has thickened sufficiently to coat the back of the spoon.
3. Remove the bowl of custard from the saucepan and stir in the yoghurt and vanilla.
4. Peel and slice the banana and mix it with the raspberries. Divide the fruit between four 1/4 pint ramekin dishes. Pour a share of the custard into each dish, leave to cool, then put in the refrigerator for about 1 1/2 hours, until very cold.
5. Sprinkle the sugar evenly over the top of the four dishes, leave to stand for 5 minutes, then put under a hot grill for only about 20 seconds to melt and brown the sugar. Serve immediately, or return to the refrigerator to keep chilled until serving time.
