To make the custard place the whole milk milk, cream and vanilla pod with its seeds scraped out together in a saucepan. Place on a medium heat and stir as it comes up to a boil. Take it off the heat before it boils.
In a bow whisk the eggs and extra yolk with the caster sugar.
Slowly pour the warm milk and egg mixture over the eggs, stirring constantly until smooth.
Grease a large ovenproof dish approximately 32cm long. I used melted butter and pastry brush to paint it on.
Butter the bread on each side. Cut the crusts off from the bread slices and cut diagonally to make triangles.
Layer the triangles in the dish with the points upwards.
Scatter the blueberries in the dish.
Zest the lemon and sprinkle over the top.
Remove the vanilla pod from the custard and pour the warm mix over the pudding.
Leave to soak for at least 30 mins.
Heat oven to 180C (160C fan).
Bake for 35-40 mins until golden brown.
Serve straight away. Keep any left overs in the fridge and eat within a few days.