Whisk the eggs and sugar together until light and fluffy.
Mix the nuts and cinnamon and fold into the egg mixture.
Pour into a well buttered and floured tart tin (23 to 25cm diameter)
Fan out the apple slices attractively on top.
Bake for 20 to 30 minutes, watching carefully from 17 minutes. When a skewer in the centre comes out clean, it's cooked.
Dust with icing sugar.
Notes
Santiago means Saint Iago or St James. The original apple-less tart by Claudia Roden would have the shape of a cross of St James picked out, via a template, in icing sugar.