Layered crepe cakes aren't difficult to make, but they do need several hours to firm up in the fridge. You can make your own mango jam, or buy it.
Make the crepes. Melt the butter and cool it to lukewarm.
In a large bowl, whisk the flour with the sugar and salt. In a separate bowl, whisk the eggs, then add the melted butter and whisk again. Whisk in the milk.
Add about three-quarters of the liquid ingredients into the bowl holding the flour, then whisk until smooth. Add the remaining liquid and whisk again. The mixture shouldn't have any lumps; if it does, strain it through a fine sieve. Cover the bowl then refrigerate for at least three hours.
Pour about 30ml (2tbsp) of cooking oil into a small bowl and place it by the stove. Heat an 18cm (7in) crepe pan (or skillet) over a medium flame. Dip a paper towel in the oil and use it to very lightly grease the pan. Stir the crepe batter then test the consistency by pouring some into the pan and swirling it. If the batter spreads out into a thin layer, it's fine; if the layer is too thick, whisk in more milk.
When the consistency is correct, ladle about 40ml (1½oz) of batter into the pan. Quickly swirl the pan to coat it lightly and pour off any excess batter. Cook the crepe until it's ready to flip: the surface will be matte instead of shiny, and it should be thin enough to see the bottom browning. Flip the crepe and cook the second side briefly, then transfer it to a plate. Repeat with the remaining batter, each time stirring gently before pouring it into the pan, and lightly oiling the pan after making each crepe. Stack the crepes as they're cooked. You should have at least 12. Let them cool completely.
Purée the mango jam in a food processor or blender (or use an immersion blender). Add the salt and clotted cream and process until combined.
Lay one crepe in an 18cm (7 in) springform pan and spread evenly with 100g (3½oz) of the mango-cream mixture. Repeat the layers, using 12 crepes and 11 layers of filling, ending with a top layer of crepe. Chill the cake in the pan for at least six hours.
Remove the sides of the springform pan. Invert the cake onto a serving plate so the bottom (which is the flattest side) is uppermost, then remove the base of the pan.
Whip the cream with the sugar until it forms medium peaks, then spread it smoothly over the sides and top of the cake. Put the excess cream into a piping bag fitted with a fluted tip and decorate the top.
Chill for at least an hour, then decorate with mangoes and other fruit. To serve, use a serrated knife to cut the cake into wedges.