Add the softened butter and sugar to a food processor. Pulse until well combined and there are no lumps of butter.
First, add the whole egg to the creamed mixture with the food processor running, and pulse until combined. Then add the egg yolk and vanilla and pulse again.
Sift together the flour and salt and add this flour mixture to the egg and butter mixture all at once. Pulse until a dough forms, do not overmix.
Remove the dough from the food processor, cover it in plastic wrap, and refrigerate for an hour.
Preheat the oven to 160°C (320°F) and line two large baking trays with parchment paper.
Remove the chilled dough from the fridge and roll it out on a floured work surface to a thickness of ½ cm ( ¼ inch) using a rolling pin.
Use an assortment of Christmas cookie cutters to shape the dough, I have used snowflakes, Christmas trees, fluted circles, and stars. Choose how many cookies you’d like to fill with jam and leave some plain. Remember that the bottom cookies must be left intact if filling them, so don’t cut circles or shapes out of these ones. Place the cookies onto the prepared baking sheet in a single layer.
Bake the cookies in a preheated oven for 15 minutes or until the cookies are light golden brown. Allow the baked cookies to cool on a cooling rack.
Spread a teaspoon of jam over the cookies that will form the cookie base. Place the top cookie onto this and then dust the top of the cookie with powdered sugar as well as any remaining cookies.