First make the shortcake. Mix together in a bowl the flour, sugar, baking powder, and salt. Add the butter cut into pieces and with a pastry blender, two knives, or your fingertips, quickly break up the butter into the flour until the texture resembles oatmeal. Beat the egg into the milk and stir them into the dry ingredients to make a smooth, soft dough. Quickly knead it on a lightly floured board, no more than 1 minute, and roll it out to 1/2 or 3/4 inch thick. With the sharp edge of a glass or biscuit cutter, cut the dough into 2-1/2 inch circles and place them well apart on an ungreased cookie sheet. (The shortcake can wait up to a few hours if necessary; it is important to serve it still warm from the oven.) Combine half the blueberries (2 cups) in a pot with the sugar, lemon juice, zest, ginger, and half the rum. Cover and bring to a gentle boil. Make a paste with the remaining rum and cornstarch and stir it into hot berry mixture. Return it again to the boil, remove the pan from the heat, and stir until the liquid has thickened. Cool the mixture, then stir in the remaining berries. Taste carefully to see if it needs more seasoning. Set aside. Whip the cream until stiff and sweeten to taste with confectioners sugar. Unless you are serving it right away, cover and chill. Preheat the oven to 450 degrees. Bake the shortcake for 12 to 15 minutes, until they are just done. Let them cool somewhat, but be sure to serve them still warm. To serve, split the shortcake, spoon some of the berries and juice over the bottom, top with a generous dollop of whipped cream, and set the cap on top. If you like, dust the top with more confectioners sugar and pass extra cream on the side. NOTES : In this variation on the strawberry classic, the blueberry filling, with half the berries cooked and half added later uncooked, is deliciously juicy, yet the fruit keeps its integrity. This filling also works well spooned into a prebaked tart shell. Recipe by: A Feast Of Fruits Posted to MC-Recipe Digest V1 #1048 by "Marie Smith" on Jan 27, 1998