First, lightly coat 6 serving ramekins or cups with butter. Set aside on the baking tray lined with parchment paper.
In a saucepan, over a medium to low heat, bring the milk to a simmer then add the vanilla extract and coffee. In the meantime, in a large bowl, place the egg yolk, egg and caster sugar. Whisk until pale and fluffy.
When the milk is warm, pour onto the egg mixture and stir to combine. Don’t be tempted to whisk the mixture, the liquid needs to be bubble free on top.
Pour the mixture into the ramekins, and fill the baking tray with warm water until half way up the side of the ramekins. Place in the oven and bake for 30 -40minutes. Remove from the oven, leave to cool for 30 minutes at room temperature and place to set in the fridge for 1 hour.