First you need to take a large dish and beat butter and powdered sugar in it. You should beat it for 2-3 minutes, at high speed, until it is light and fluffy. Add vanilla and beat some more, until it is well combined.

After that, lower the speed and add flour, cornstarch and salt and beat until just incorporated, do not over-mix. Cover the batter with plastic foliage and chill for 30 min and then it should be taken out of the fridge. Preheat the oven to 325 F. Then, take two baking sheets and line them with parchment paper.

Begin making 1 inch balls that should be placed in the baking sheet that you have already prepared. Then, press each ball in the center, with a finger or ½ tsp. measuring spoon, so to make a  indentation.

It is really important to be careful while doing this, because the batter could crack, although it is pretty soft. If it happens, anyway, you can even or close the crack with your fingers.

Next, you need to put the jam filling in the center and bake for about 20 minutes.

After 20 min, take the cookies out of the oven and leave them to cool in the baking sheets for a few minutes, and then transfer them to a wire rack and sprinkle with powdered sugar.