First, the dough! Dutch process cocoa powder, flour, sugar, and salt in a food processor, then chopped up pieces of cold butter and ice water. You just get to the point where it is crumbly, then pat it out with the heel of your hand with some pressure.
Then pat into a rectangle and chill.
King Arthur Flour shop when I took a pizza making class up there). I know enough about pie crust not to force it into the pan. I think you really need to just lower it in, and not pull it at all. There was much discussion here as to why the recipe asks to remove the bottoms of the pans. I did this and it worked fine. I think also if you have any problems that you should ball it back up and chill that piece of dough again. I think once it goes too wrong it can't really be fixed unless it is chilled again.
For the biscotti, I considered making my own, but it just didn't seem worth it for just a few of them. Also, if you have tarts in the house you don't also want tons of biscotti. So I went with caramel macchiato biscotti I bought individually at a Starbucks.
Chop those up and white chocolate, semisweet chocolate, and bittersweet chocolate. Like I mentioned I used Ghirardelli, which I think worked really well.
This is quite a luxurious custard filling with chunks of of chocolate and biscotti bits in it. Start with melting butter with the bittersweet chocolate in a bowl set over a saucepan of boiling water.
Whip the egg yolks with vanilla extract (I think coffee extract could be a good substitution for the vanilla). Then mix a third of the egg yolks with the chocolate, and fold them altogether.
Then after you spread the filling in your tart crusts, and bake them you've got these lovely, luxurious, over the top desserts.
Very delicious! As I said, also laborious and incredibly rich - but for company this would be a great recipe! I thought they also had a nice flavor the next day. Check out all the other bakers' tartlets here!