in a bowl, mix the wet ingredients using a whisk until incorporated.
add the sugar and whisk until dissolved add the cornflour and salt and continue whisking.
gradually add the sifted flour to the mix and incorporate it with your hand, in this step make sure not to knead the dough.
rest the dough for 30 minutes till firm and cold, flatten the dough with a roller pin on a floured surface, the thickness should be around 3 - 4 mm.
cut the dough with a round pastry cutter, in the center of the circle, put a tsp of jam and meet the two ends, use a fork to seal it.
line the cooking rack with parchment paper and bake for 15-20 min in a 180°C oven, or until golden on top, it's okay if the jam got out from the sealed sides, it should be just fine and still tasty.