Preheat the oven to 200 degrees. Grease 8 tartlet molds (10-12 cm in diameter) with butter.
In a bowl, beat 125 g of soft butter with sugar and eggs until frothy. Add the almonds, flour, baking powder and lemon zest and stir in. Pour in the coconut milk and mix everything into a smooth dough. Peel the mangoes and cut the flesh from the stone in thin wedges.
Distribute the dough evenly on the molds and smooth it out. Place the mango slices on top in a rosette shape. Mix the vanilla sugar and desiccated coconut and sprinkle the tartlets with it.
Bake the tartlets for about 20 minutes. Remove and allow to cool almost completely in the molds.
Remove the tartlets from the molds and serve lukewarm or cold with crème fraîche.