Add strong bread flour, yeast, salt and caster sugar to the bowl of a mixer fitted with a paddle (or bladed paddle). Add eggs, tepid milk and vanilla extract and mix on low speed to combine.
Slowly add the small butter pieces, one at a time. Now swap the blade for the dough hook and mix on medium to high speed for 5mins.
Turn dough out into a lightly oiled bowl and cover with cling film, place in fridge for a minimum of 5 hours or ideally overnight.
Remove dough from fridge and place onto a lightly floured work surface, lightly knead to form a ball, using a rolling pin roll the dough gently to fit inside an 8 inch spring form tin with the bottom removed, place the spring form tin onto a baking sheet lined with grease proof paper and place the dough into the tin to fit. Then place the whole lot inside a plastic bag and leave to prove for 1 1/2 to 2 hrs at room temperature.
Make the Creme Patisserie by first adding the gelatine sheet to a small bowl of water and put to one side. Add the eggs and sugar to a separate bowl and whisk to combine, then sift in the plain flour and corn flour. Mix well until you have smooth paste. In the mean time, heat the milk to a simmer and then add to the egg mixture a little at a time, whisking as you go, Pour the custard back into the saucepan and bring to the boil. Whisk it for a minute and once it has thickened, take it off the heat. Take the gelatine sheet and squeeze out the water now add to the custard and mix in. Once cooled, stir in the mango and lime juice. Place into a glass bowl and cover the custard directly with cling film to prevent a skin from forming. Place in the fridge until required.
Pour whipped cream into a bowl and add the sifted icing sugar, using a hand mixer or whisk mix cream until stiff, cover with cling film and place in to fridge until required
Pre-heat oven to 180c fan. Remove the proved dough in its tin and on the baking sheet from plastic bag and egg wash the brioche surface. If using Pearl sugar, sprinkle on top at this point. Bake in oven for 25-30 mins until golden brown.
Remove from oven and allow to cool slightly before removing the spring form cake tin. Place on to a cooling rack to fully cool.
Using a sharp serrated knife slice the brioche horizontally through the middle. Take the mango Creme Patisserie and Chantilly cream and gently combine using a spatula to combine. Place the mixture into a piping bag fitted with a large plain tip nozzle, pipe drops of cream all around the edge of the bottom of one half working in wards to cover the base. Place the top half on to the creamed base, and add desiccated coconut if pearl sugar was not used then add sifted icing sugar to the top.