Whisk the yolks together with the sugar, lemon juice, cornflour and mango puree in a heatproof bowl over a saucepan of simmering water (double boiler). Continue to whisk or mix with a spatula for about 5 minutes till the eggs are cooked and the mixture thickens to a creamy consistency.
Take the bowl off the heat and whisk in the butter till fully incorporated. Place a piece of cling film to on the surface of the curd so that it fully covers it; this will prevent a ‘skin’ from forming while it cools.
Cool the mixture and chill in the fridge for 2-3 hours till it firms up to a custardy texture.
To make the cake
Preheat your oven to 175℃. Lightly grease a 9-inch springform pan and dust with flour, making sure to remove the excess flour. I line the bottom with a slightly oversized baking parchment before I grease and flour. It helps to transfer the cake to a plate / stand more easily.
Using a stand mixer or hand mixer, cream the butter and sugar till light and fluffy.
Sift the whole wheat and oat flours together with the salt and baking powder in a separate bowl. Add it to the butter mixture.
Beat the eggs separately till foamy. Take care not to overbeat.
Add the eggs to the butter-sugar mixture, followed by the almond flour and milk
Transfer the batter to the prepared pan. Dollop spoonfulls of mango curd on the surface of the cake, sprinkle with toasted almond slices, sprinkle with a tbsp of sugar and bake for about 40 minutes. The curd should have baked and set and you should get a clean toothpick when you insert one into the cake.
Cool the cake for 10 minutes in the pan before removing it and cooling on a wire rack.