Place the milk, sugar, milk powder, glucose, vanilla & salt into a large saucepan.If you're using a vanilla pod, scrape out the seeds & add both the pod & seeds to the pan. Whisk to combine then place the saucepan over a low heat & leave to warm gently until steaming – don’t let it boil. Make sure to stir the milk regularly with a spatula.
Whilst the milk is heating up, place the yolks into a mixing bowl.
Once the milk is steaming, pour half of it into the yolks, whisking as you do so. Pour the now tempered yolks into the pan of milk.
Cook the custard over a low heat, stirring constantly with a rubber spatula until it is thick enough to coat the back of a spoon & has reached a temperature of 82°c/180°f.
Remove the custard from the heat, stir in the double cream then pass into a bowl, through a sieve. Leave to cool to room temperature, stirring regularly.
Once cool, add the blueberries into the custard, whisk to combine then give the blueberry custard a quick blitz with a stick blender. Cover the surface of the custard with a piece of baking parchment then chill in the fridge overnight.