Method

• Place the milk into a saucepan and scrape the seeds from the vanilla pod. Add both the pods and seeds to the milk. Heat the milk until it reaches a light simmer
• Take off the heat and place a fresh saucepan onto a medium heat. Once the pan is hot, slowly add in the sugar (1) a third at a time and stir with a wooden spoon to make sure each addition is melted completely before adding the next.
• Once all the sugar is melted, continue to cook until the sugar is a golden brown colour. This should only need 10-20 seconds
  Then SLOWLY add in the milk (about a quarter at a time) by pouring in a little, incorporating it into the mixture and then adding more.
  Once all the milk is in, return to a low heat and bring up to a light simmer so any sugar clumps can dissolve.
• Meanwhile, whisk together the egg yolk, egg, sugar (2) and custard powder in a heatproof bowl to a paste and when the milk mixture has reached a simmer, pour into the bowl and whisk until incorporated.
• Transfer this mix back to the pan and cook on a medium heat whilst whisking well to make sure that nothing is sticking to the bottom of the pan.
• Bring the mixture up to the boil (it should look like very thick custard) and then take off the heat.
• Add in the butter and whisk to incorporate before pouring through a sieve into a bowl or high sided tray and cover with cling film (so that it touches the top of the cream to avoid condensation).
• Set in the fridge until cold.