Put the milk, cream and sugar in a pan and heat gently until bubbles appear on the surface.
In a large bowl, beat the eggs and vanilla until creamy.
Pour the warm milk gradually over the egg mixture, while stirring constantly. When you get a smooth, thick cream add the lemon zest and set aside.
Grease a baking dish with butter.
Cut the brioche in half or quarters, then spread some butter on cut-side of each.
Arrange theses in the baking dish, letting them overlap each other.
Scatter the blueberries on top, then pour over the custard.
Let it rest for 10 mins, while you preheat the oven to 180°C.
You can sprinkle some sugar on top, if you want crunchy, caramelised crust.
Bake in the middle of the oven for 35-40 minutes.
When the top is golden and the custard has just set (it should be wobbly), then its’ ready to serve.