Dissolve the yeast in the warm milk and leave to foam for 15 minutes.
Put the flour, sugar, salt, oil and vanilla in a large bowl.
Gradually add the milk/yeast mixture.
Knead until a smooth, soft ball forms. Cover and leave to rise for 1 hour (the dough should double).
Deaerate the dough and separate into 4 balls, leave for 15 minutes. Spread the brioche dough in circles of 15 cm in diameter and about 1.5 cm thick. Leave to rise for an hour at 35°. Brush with gold and sprinkle with brown sugar or crumble mixture. Bake at 170 degrees for about 20 minutes. Leave to cool on a rack.
Boil the water with the caster sugar, orange zest, vanilla pod and orange blossom. Leave to cool.
Place the bowl of the food processor and the whisk in the freezer.
Meanwhile, prepare the custard
Put the gelatine in cold water. Put the milk in a stainless steel pan and heat it. In a bowl, whiten the egg yolks with the caster sugar. Add the cornflour and whisk. When the milk is hot, pour it over the mixture while whisking, then pour it back into the saucepan and heat it again without stopping whisking. When the mixture thickens well, whisk again for 1 minute then remove from the heat. Squeeze out the gelatine and whisk it into the pan. Pour the mixture into a large dish, cover with plastic wrap and leave to cool for 2? hours at room temperature.
Take the bowl out of the freezer with the whisk. Pour in the mascarpone and the cream. Whip until you have a stiff whipped cream. Place in the refrigerator until cool.
Once the cream has cooled, add the rum and whip it in a food processor for a few seconds to make it smooth. Then add a good tablespoon of cold whipped cream and whip again until you have a nice cream. Finally, add the rest of the whipped cream and gently fold it in with a Maryse blade, lifting and turning the bowl. Pour into a pastry bag fitted with a plain tip N°13. Set aside in a cool place for at least 1 hour.
Cut your cake in half, soak both sides with the warm syrup. Garnish with the cream. Divide the drained pineapple pieces between them. Cover with a little cream, zest your lemon and cover with the top of the cake. Set aside for at least 1 hour before eating.