How to Make It
In a food processor, pulse the two flours with the butter and salt until the mixture is the texture of wet sand. Add the egg yolks and 1 tablespoon of water and pulse until the dough just comes together in a ball. Transfer to a work surface and pat into a 3-by-6-inch rectangle. Wrap in plastic and refrigerate until firm, at least 30 minutes.
Butter a 4-by-14-inch fluted rectangular tart pan with a removable bottom. Set the dough between 2 sheets of plastic wrap; roll out to a 6-by-16-inch rectangle. Discard the top sheet of plastic wrap and invert the dough into the prepared pan. Gently press into the corners and up the sides of the pan. Discard the plastic wrap and trim the overhanging dough flush with the rim. Refrigerate until firm, at least 15 minutes.
Preheat the oven to 375°. Line the tart shell with parchment paper and fill with pie weights or dried beans. Bake for 15 minutes. Remove the parchment and pie weights and brush the tart shell with the beaten egg. Bake for about 5 more minutes, until set. Let cool slightly. Reduce the oven temperature to 350°.
In a food processor, combine the walnuts and sugar; process until finely chopped. Add the butter, egg, tapioca flour, cream, Grand Marnier, clementine zest and salt and pulse until smooth. Scrape the frangipane into a bowl; chill until firm, 30 minutes.
In a food processor, combine the cranberries, sugar and clementine juice and pulse just until the cranberries begin to break up.
Spread the frangipane in the tart shell and top with the cranberries. Set the tart on a rimmed baking sheet and bake, rotating once, until the frangipane is puffed and lightly browned at the edges, 30 to 35 minutes. Transfer to a rack and let cool. Unmold and serve.