For the cream filling: Cream together the butter and sugar until light and fluffy. Stir in the almonds, then the egg, rum and vanilla. Beat until smooth with a fork. Cover and chill until firm, at least 1 hour.
For the pastry shell: Lay an 8-inch/20 cm round plate on one sheet of cold pastry and go around it with a knife. Do the same for the top round, but then roll this one a little with a rolling pin to make it slightly larger than the bottom round. Lay the smaller round of chilled dough on a dampened baking sheet. Spread the chilled cream filling over, leaving a good 1-inch/2.5 cm margin all around the edge. Hide a bean somewhere in the cream. Brush the border with egg wash. Lay on the top round and press the edges well to seal. Score the edge all around with the blunt side of a knife to seal. Make a cross in the center for steam to escape and draw spirals out to the edges for decoration. Brush with egg wash all over the top, avoiding the edges, so that they'll puff up easily. Chill in the freezer until very firm, about 20 minutes.
Preheat the oven to 450 degrees F/230 degrees C. Bake the cake until puffed up high and dark golden in color. Sprinkle with a thin coating of confectioners' sugar and blast under the broiler or melt with a blowtorch. You can also brush with melted apricot jam for a glaze.
Recipe courtesy of Laura Calder