Preheat the oven to 170°C and grease a 30x20cm baking tin lined with parchment.
Spread 2 tablespoons of agave nectar on the tin base and arrange pineapple rings with cherries.
Sift flour and salt into a bowl, making a well for melted butter, agave, and eggs.
Fold the mixture gently and pour over the fruit, smoothing the top with a spoon.
Bake for 35 to 40 minutes at 170°C until a skewer comes out clean.
Cool in the tin for 5 minutes before turning out onto a rack and drizzling with agave.
Heat milk, maple syrup, vanilla extract, and seeds in a saucepan until almost boiling.
Beat egg yolks and cornflour together, then temper with ladles of the hot milk mixture.
Return the mixture to the pan and stir over medium heat until thickened.
Serve slices of cake with the warm custard poured over.