This truffle tart is simplicity itself with very few ingredients. So it’s important to use the freshest nuts you can and the highest quality chocolate. The tart will keep in the refrigerator for up to two days before serving. If you choose to decorate it with spun sugar designs, as is suggested in the tip, be sure to place the designs on the tart just before serving. Otherwise they will melt into the chocolate filling.
Preheat the oven to 350°F.
Place the pecans and sugar into the bowl of a food processor fitted with the metal “S” blade. Pulse together until the pecans are finely ground. Pour in the melted margarine and pulse again until the mixture is thoroughly moistened – it will seem a touch greasy.
Place the tart pan on a baking sheet (some of the margarine may seep through) and bake in the center of the preheated oven for 15 minutes. Transfer to a rack to cool completely.
Press the pecan mixture onto the bottom and up the sides of a 9- or 10-inch tart pan with a removable bottom.
Heat the cream in a saucepan just until bubbles appear around the edge. Pour about ¼ cup of the mixture into the egg yolks, whisking constantly. Whisk in the remaining cream. Pour the mixture over the chopped chocolate, whisking until the chocolate is melted and smooth. Whisk in the vanilla. Pour into the cooled shell.
Cover lightly and refrigerate for at least 8 hours or for up to 2 days.
Decorate with cocoa powder, additional pecans or candied pecans.
For an extra special touch, pour about 1/3 cup granulated sugar into a small, heavy-bottomed saucepan. Pour in 3 tablespoons water. Bring to a boil over medium-high heat until the sugar is dissolved. Increase heat to high and boil, brushing down the sides of the pot occasionally with a brush dipped in water, until the mixture turns an even caramel or amber color. Immediately submerge the bottom of the saucepan into a large bowl of ice cold water. This will stop the cooking process. Let the caramel cool slightly. Then, dip a spoon into the cooled caramel. Let the caramel drizzle from the spoon onto a piece of parchment paper, making a decorative design as you drizzle the sugar. Repeat a number of times. Let the caramel cool. Just before serving, transfer the spun sugar designs onto the tart.