beat the butter and icing sugar
Beat the butter and icing sugar until fluffy, about 3 minutes. Add the eggs (one by one) and rum. Beat until combined.
Meanwhile whisk together the flour, baking soda, zest of one lemon, pinch of salt, seeds of 1/2 vanilla bean. You can also add chopped cardamom. Add the flour mixture to the egg mixture and mix until just combine. Wrap in plastic wrap, and refrigerate for about 30 minutes.
Lightly flour the surface and roll out the dough about 3mm thick (1/4"). Using a linzer cookie cutter, cut out the cookies. Transfer them to a baking sheet, lined with parchment paper. Bake for about 10 - 12 minutes at 190 °C / 375 °F, or until golden brown. Transfer to a rack to cool completely.
serve and store
Pour marmalade into a saucepan and heat slightly. Spoon 1 teaspoon of jam into the center of a cookie, spreading it slightly. Top with sugar dusted cookie with a whole. Serve right away or store in a box for up to 10 days.