In a mixing bowl, stir in plain flour and icing sugar.
Quickly cut in frozen butter that has been cubed into the dry mixture using a fork or pastry cutter. If you have a food processor, this process can be even faster by quickly blitzing until crumbly.
Then, mix in egg yolk until the dough turns into sandy chunks.
Transfer onto a surface and quickly shape it into a disk. Let it chill in the freeze for at least 30 minutes.
Once your dough has been chilled, portion out around 12 to 15 grams of dough and roll it into a ball. Dust well with plain flour and transfer onto your baking tray that has been lined with a parchment paper.
Press the dough into a pineapple tart mold that has been dusted with flour.
Carefully remove the dough from the mold with your hands and place it neatly onto the tray.
Once it is done, preheat your Rowenta oven to 180C, fan-forced.
Freeze your dough for about 20 minutes before putting it into the oven.
Bake it in the oven for about 10 minutes.
Once it is baked, let the cookie cool down for awhile, then turn down your oven to 160C, fan-forced.
Pipe out Nutella onto the cookie base using a star tip. If you like your shape to be more defined, you may put the Nutella in the fridge for awhile to firm up.
Bake it in the oven for about another 9 to 10 minutes at 160C until Nutella has firm up.
Let it cool completely before transferring into airtight container. I like to cool it individually in the fridge for a while before stacking it up in the container and store it in the fridge.