Apple Crumble and Pineapple Tarts

Yes, there are two distinct recipes here. Click here for apple crumble, and here for pineapple tarts (please see important note at bottom of post). I had recommended 2 egg yolks instead of 1 for the dough for the tarts, but on a second attempt, the biscuit base turned out too crumbly. I'm guessing that I should have stuck to the recipe, or perhaps just added half a yolk more. Does anyone know the effect of egg yolk on the dough, other than the binding function it serves? (Warning, these are links another blog of ours, which links to the actual recipes. Included here for completeness.)

* IMPORTANT: Please refer to "The Correct Recipe for Pineapple Tarts" which overrides the one on Star Kuali we had originally linked to. Sorry Amy Beh, but maybe your pastry recipe just does not work for me...