Spitzbuben jam biscuits with lingonberry preserve

I attended Manuel Marzari's Not Just Christmas Biscuits course and will share more recipes. Interesting, simple recipes that work by following the steps and advice. I have tried many shortcrust recipes, but this surprised me with its lightness. Lovely for Christmas and small gifts.
INGREDIENTS
200 G ITALIAN 00 FLOUR
120 G ROOM-TEMPERATURE BUTTER
6O G SUGAR
30 ML EGG
2 G CREAM OF TARTAR
2 G BICARBONATE OF SODA (OR 4 G BAKING POWDER)
1 PINCH VANILLA POWDER OR SEEDS OF 1 POD
1 PINCH SALT
GRATED ZEST OF HALF AN ORANGEI remove butter from the fridge a few hours ahead to soften and mix easily. The egg should be room temperature too. I beat the whole egg in a small bowl.I measure only 30 ml.I sift flour with raising agent.I add sugar and vanilla powder.I quickly rub in butter into crumbs and add a pinch of salt.I grate half an orange's zest.I add egg.I quickly mix by hand. Until smooth.I flatten the dough block.I wrap in parchment or cling film and refrigerate at least half an hour.I take it out.I roll about 5 millimetres thick. With correctly weighed ingredients and method, extra flour is unnecessary; parchment on top helps rolling.I cut biscuits with a cutter.I arrange on a parchment-lined tray and cut holes in half for the tops.I gather scraps and reroll, chilling before reuse.I prepare all and heat oven to 160°C.I bake about 15 minutes, checking so they do not brown too much.I cool, turn whole biscuits over and dust holed ones with icing sugar.I pipe a little preserve onto each base.I sandwich pairs together.I store in a cool, dry place, ideally a tin.