Preheat oven to 350 degrees F convection. Line bottom of an 8in cake pan with parchment paper and brush melted butter on the paper.
Cream together the butter, vegetable oil and sugar until pale and fluffy. Beat in two full eggs and two yolks-only(!), one at a time. Then mix in the mango pulp.
Mix in the flour and baking powder. Pour batter into the pan.
Bake for 50-55 minutes. Test after 45 minutes by shaking the pan slightly and see the center is solid, and the edges are starting to pull away from the pan. Leave to cool before adding the curd.
Mango curd. Can be prepared ahead of time as must be cooled.
Whisk together the mango pulp, egg yolks, sugar, cornstarch, and salt in a thick bottomed sauce pan.
Heat gently, stirring continuously, until it suddenly thickens. Don't heat for more than 30 seconds beyond the thickening.
Remove from heat and stir in the butter, until melted. Immediately pour through a strainer to remove any egg solids. Then put in the fridge to cool.
When the cake is cooled, slice in half horizontally. Spoon the chilled mango curd on the lower half. I think a bit of curd spilling out adds good color! Place the upper half on top!
Prepare the mango glaze by combining the mango juice and last sugar ingredient in a saucepan. Heat gently to boiling, stir regularly, continuing to boil.
As it boils it will slightly thicken. When the spoon can pour and show it is no longer runny, remove from heat and immediately spoon over the cake. The mixture will solidify quickly so don't hesitate. Don't try to spread, just pour from the spoon!