Preheat oven to 150 degrees celsius and grease a 24 cm x 4cm tart or quiche dish.

For the pastry:
In a bowl, sieve together the dry ingredients for the pastry. Rub in the butter until mixture resembles fine breadcrumbs.
Mix the egg and vanilla essence together then pour into sieved ingredients, mix until the mixture forms a dough. Roll dough thinly out onto a lightly floured surface, making sure it is big enough to fit the tart dish. Line tart dish with pastry and leave in the fridge until needed.

For the filling:
Place butter and dark chocolate into a glass bowl and place over a double boiler, allow to melt. Whisk the eggs and caster sugar together until light and fluffy (eggs should triple in volume and go a light pale yellow colour), best to use a hand held beater or Thermomix if you have one.
Fold in the flour, followed by the warm chocolate. Pour chocolate mixture into chilled lined pastry tart dish and bake for 35-40 minutes.
Once cooked, take out the oven and allow to cool. The filling and crust will sink, flatten the filling down gently around the sides to help even out the top.

For the topping/ganache:
Pour the cream and milk chocolate into a glass bowl and allow to melt over a double boiler. Mix after 2 minutes until a silky smooth texture forms and the chocolate has melted. Pour over cooled tart mixture, making sure the ganache fills the entire top of the tart. Leave to cool for a few hours before serving with cream or ice cream.