This classic tart, essentially a frangipane filling enclosed between two layers of puff pastry, is named for the French town in which it was created.
Make the frangipane: In the bowl of a food processor fitted with the metal blade, process almonds and sugar until mixture is very fine crumbs. With the machine running, add 2 egg yolks, butter, and rum; continue processing until mixture is smooth and combined.
On a lightly floured work surface, roll out pastry dough into a rectangle at least 9 1/4 by 18 1/2 inches and about 1/8 inch thick. Using a 9-inch round cake pan as a guide, cut out two 9-inch rounds.
In a small bowl, whisk together remaining egg yolk and cream for the egg wash. Place one round on a baking sheet, and spread almond mixture on top, leaving a 1-inch border all around; brush border with egg wash. Using an aspic or cookie cutter, cut a 1/2-inch hole in the center of remaining round; place cut round on top of other round, pressing lightly around filling to seal rounds together. Place in refrigerator 1 hour.
Preheat oven to 425 degrees. Remove tart from refrigerator; using a small paring knife, score the top by making curved lines from the center to the edges like a pinwheel. Brush top of tart with the egg wash, being careful not to let any excess drip down over cut edge of dough, as it will inhibit proper rising. Return to refrigerator to chill again, if needed.
Place baking sheet in oven, and bake 30 minutes. Reduce heat to 375 degrees; loosely cover tart with aluminum foil, and continue cooking 30 minutes more.
Transfer to a wire rack, and let sit 20 minutes. Remove tart from pan by sliding it onto a serving platter. Serve warm or at room temperature, cut into wedges.
We recommend using an insulated baking sheet instead of a regular baking sheet to prevent the bottom from getting too browned during baking.