The original tart uses a crumb crust made of digestive biscuits. Digestives are plain tea time cookies ("biscuits") from England. I love them. I suppose the closest thing we have to a digestive in this country is a graham cracker. But I have to say a graham cracker is a poor imitation—there is much more substance and flavor to a digestive than there is to a graham cracker. Having said that, I didn't happen to have any digestives on hand...if I ever have them around, I eat them...so I made a simple graham cracker crust instead. If you have the time and the inclination, the digestives are worth seeking out. McVitie's is my favorite brand. Simply use the crust recipe in the original recipe, remembering to increase it by half.
The filling of the tart is nothing more than ganache, reinforced with egg yolks. Classic ganache is made with equal quantities of heavy cream and chocolate. The cream is brought to a simmer and then poured over the chopped chocolate. The heat of the cream melts the chocolate—all you have to do is whisk or stir it until it is smooth. At room temperature, ganache holds a soft shape. Like ganache, the filling for the tart is made of equal quantities of heavy cream and chocolate, but instead of pouring the hot cream directly over the chocolate it is first combined and cooked briefly with some egg yolks. This thickens the cream and helps the final tart filling set up firmly enough to cut cleanly and hold its shape at room temperature.
Be careful when you are cooking the yolk-cream mixture. It will thicken very quickly—especially if you accidentally allowed the cream to come to a full boil before adding it to the yolks. If the yolk-cream mixture gets hotter than 180°, you will have scrambled yolks floating in cream rather than a nice thick creamy custard.
Since ganache is what truffles are made of, I decided to call my dessert "Chocolate Truffle Squares with Candied Orange Peel". And since truffles can be flavored with all kinds of things, the possibilities for flavor variations are almost without limit. I love chocolate and orange together, but maybe next time I will make Mocha Truffle Squares, or Chocolate Truffle Squares with Praline, or...
Chocolate Truffle Squares with Candied Orange Peel
Graham Cracker Crust:
7 1/2 oz. graham crackers, finely ground (to make 2 cups crumbs)
4 1/2 T. granulated sugar
7 1/2 T. unsalted butter, melted (see note)
Line a 13- by 9-inch baking pan (or a quarter sheet pan) with foil, leaving an overhang. Butter or spray the foil. Combine the crust ingredients until homogenous and press into the pan in a compact even layer.
|Use a measuring cup (or some other flat-bottomed glass or mug) to press the crumbs into a compact even layer|
Bake in a pre-heated 350° oven until just beginning to brown—10 to 12 minutes. Cool.
3 large egg yolks
2 c. heavy cream (450 g.)
16 oz. (450 g.) fine-quality bittersweet chocolate (no more than 60%), finely chopped
3/4 c. (125 g.) finely chopped candied orange peel, plus extra for garnish
Lightly beat yolks in a small bowl. Bring cream to a simmer in a 2-quart heavy, saucepan and remove from heat. Add about one third of hot cream to yolks in a slow, thin stream, whisking constantly, then pour yolk mixture into remaining cream, whisking.
Return the custard to a moderately low heat and cook, stirring constantly with a wooden spoon or heat-proof rubber spatula, until it is thick enough to coat back of spoon and registers 170°F on thermometer, 1 to 2 minutes (do not let boil). Remove from heat and add chopped chocolate, whisking until smooth. Stir in chopped candied peel.
Pour filling evenly over crust and chill, uncovered, until firm, at least 2 hours. Lift out of the pan using the foil, trim the edges and cut into 48 small squares, using a thin sharp knife. For beautiful clean-edged squares, dip the knife into hot water and wipe it clean on a towel in between each cut.
Garnish each square with some of the reserved chopped candied peel. Serve chilled or at cool room temperature.
(Recipe adapted from Gourmet Magazine, January 2005)
Note (added 1 Jan 2011): Crust recipe as originally posted called for 6 T. melted butter. I have changed it to 7 1/2 T. The larger amount of butter makes the crust easier to work with—both when pressing it into the pan, and when slicing and serving the truffle squares.