Pour the milk in to a large saucepan and bring gently to a simmering point. Don't boil!
Place the eldeflowers in the milk - flowers down and leave to infuse for about 20 minutes.
Pour the milk and elderflowers through a fine sieve and discard the elderflowers.
Pour about 1/3 of the milk into a large jug or a bowl.
Add the cornstarch to the milk in the bowl and mix with a whisk until it's completely smooth.
Add the sugar and tiny pinch of salt to the saucepan with the majority of the milk.
Bring the milk slowly to the boil, stirring occasionally and making sure that the sugar has dissolved completely.
When the milk is nearly simmering, pour the remainder of the milk with the cornstarch in and continue to stir with a whisk. Work fast, as the mixture will thicken very quickly at this point. Carry on boiling until bubbles appear on the top and the whole mixture is nice and thick. This usually doesn't take more than a minute.
Pour straightaway into pudding bowls or glasses and leave a little gap on the top for elderflower cordial, lemon curd or any other toppings.
Leave to cool down at room temperature and then place in the fridge for a further hour or so.
Best served on the same day or within 2-3 days (max). Keep in the fridge and serve straight from the bowl or gently turn out on the plate.