First of all, prepare the shortcrust pastry: work the flour with the vanilla and chunks of butter cold from the fridge.
Then quickly add sugar and bicarbonate, and finally the yolk.

Once you have a smooth and homogeneous dough, wrap it in cling film and let it rest in the fridge for at least 1 hour.

Take the dough, roll it out on a lightly floured pastry board and cut out the molds you prefer (possibly similar in size, for a more even cooking): I chose Santa Claus hats, snowflakes and simple balls.
Place them gradually on a baking sheet lined with parchment paper, then bake for about 10 minutes or until golden brown in a preheated convection oven at 180 ° C.

Color the sugar paste to taste with food coloring, then roll it out and start cutting out your decorations.

I created mini candy cane in sugar paste (with white and red pdz) to attach to the green balls.

And some small holly decorations (with red and green pdz) to attach to the red balls.
In addition, I created Santa Claus hats with white pdz on a red base, and I covered the snowflakes with white pdz, sticking the sugars on them.

I recommend: use the food gelatin to attach the sugar paste to the biscuits and to attach the decorations on the pdz bases, then let it rest for a few hours so that everything dries well.

The sugar paste Christmas cookies are ready.