Oh well, I called them shortbread because they aren't cookies to me, ah ! They are really rich & buttery, with a nice vanilla flavor.
In case you'd like to bake them too, here is the recipe, which made 24 really big & thick shortbreads. (or twice as much but twice smaller !!)
250 g (1 cup) unsalted butter, diced
150 g (3/4 of a cup) blonde sugar
300 g (over 2 cups) flour (+ for flouring your table)
2 teaspoons vanilla extract
a dash of salt
one egg yolk
In a bowl, mix the butter (cut into small dices) and the sugar. Add the vanilla extract & egg yolk & mix in very well. Finally add the flour & the salt, and make a ball of dough. Wrap in cellophane & put into the fridge for 30mn.
20 minutes later, preheat your oven at 180°C/350°F. ... Take the ball out of the fridge (or half of it if you're baking with children), roll it flat but not too thin, on a floured surface. (keep extra flour at reach, you'll need it) Cut biscuits with a cookie cutter of your choice. We used a round one, and used a baking stamp after that. Try as much as possible to make them all of the same thickness.
Lay them on a parchment paper on the oven grid, and put in the over for at least 15mn. Beware, if your shortbreads are thin, they will need a little less, and if they're thick, they'll probably need a bunch more. (like for mine) Check regularly, they must not turn too brown !
Take them out of the oven but don't touch them, let them cool on the oven grid, for at least 10mn before thinking manipulating them. Then manipulate them carefully & delicately ... Eat some right away, and store the rest in an air tight container ! Just a note : they are not the dry & crunchy type of biscuits (in case that's what you're looking for), they're more of the chewy & tender type !