Iced Orange Shortbread Cookies
Combine the flour, cold butter, 100 g (approximately 1 cup) of powdered sugar, vanilla sugar, egg yolks, a pinch of salt and the orange zest in a large bowl. Mix everything together using a pastry cutter or two forks, then quickly knead with hands until smooth. Wrap with plastic wrap and refrigerate for about 30 minutes.
Preheat the oven to 200°C (approximately 400°F). Line a baking sheet with parchment paper.
Roll the dough between 2 layers of plastic wrap to about 2 mm (approximately 1/10 inch) thick. Using a cookie cutter, cut into heart shapes about 5 cm (approximately 2 inches) wide.
Place the cookies onto the prepared baking sheet and bake for 10 minutes, until golden brown.
Remove from the oven and allow to cool slightly.
Spread a layer of orange marmalade onto half of the cookies and top with the remaining cookies.
Whisk the remaining powdered sugar with the Grand Marnier and egg white until smooth. Transfer the mixture to a freezer bag and make a small cut in the corner of the bag.
Pipe the icing onto the cookies in a decorative pattern, allow to the icing to harden and store the cookies in an airtight container.