Preheat the oven to 180°C / 350℉.
In a large mixing bowl, mix the butter with an electric mixer until it is light and fluffy. But make sure not to overmix it.
Add the sugar and continue mixing on medium speed until you have a creamy texture.
Now add the whole egg and incorporate into the sugar/butter mixture.
Add the flour and ground pecans and vanilla extract.
Continue mixing until you have a firm cookie dough.
Shape dough into a disc and place it in a plastic wrap. Refrigerate for at least an hour but best overnight.
Gently flour your countertop, take the flour out of the fridge and place on the countertop. Put some flour on top of the dough and roll it with a rolling pin until you have 1 cm thick dough. An alternative is to roll the dough between two pieces of parchment paper.
Now place the dough back in the refrigerator for 30 minutes or the freezer for 5 minutes.
In the meantime, line a baking tray with parchment paper.
Take out the dough from the fridge/freezer and using cookie cutters cut out sand tarts cookies.
Place the cookies on the baking tray.
Bake for 8 - 10 minutes.
Once finished, take out of the oven and let them cool for 5 minutes in the baking tray and sprinkle with powdered sugar while they are warm and place on a wire rack to fully cool.
Serve as dessert, with coffee/tea or on a holiday cookie platter.