Cut the butter into smaller pieces and place it together with flour, powdered sugar, vanilla, and salt in a mixing bowl. Mix well until the butter is crumbled. Stir the egg yolks into the flour mixture, and bring the dough together on the table, using a light hand. Roll out the dough on a floured surface to a thickness of about 2 millimeters. Cut out rings using a 6 cm diameter cutter. Cut strips with a height of 2.5 cm and a length of about 15 cm. Place the tart rings on a baking sheet lined with parchment paper. Place a base in each tart ring. Roll the long strips and place them in the tart ring, then roll it out along the edge. Cut off the excess strip and press the seams together. Bake the tart shells for 20-25 minutes at 155 degrees Celsius (311 degrees Fahrenheit) in a conventional oven, in the middle of the oven. After baking, release the tart shells from the tart rings and let them cool on a wire rack. From this portion of dough, you can make 12 tart shells. While the first batch of tart shells bakes, place the dough in the fridge.