Take butter, sugar and vanilla in a bowl and whip till creamy.
Add in flour, baking powder and salt and whip again till it is mixed into a soft dough.
Now wrap this in plastic and chill this for couple of hours.
Once the dough is chilled. Cut it in half.
Now preheat oven to 180 degree C.
Roll the dough into ¼ inch thickness and use a round cutter to cut out circles. Now use smaller cookie cutter to cut out some of the round circles to create a window pattern through which the jam can show when they are sandwiched.
Arrange it in a parchment lined baking tray.
Bake for 12 to 15 mins. If your cookies are thicker it may take upto 15 mins.
Now remove it from oven and cool it down completely.
Now take the whole cookies and arrange it bottom size up on a plate. Smear jam over it, now in the cut out top cookies sprinkle with icing sugar. Now sandwich the cookies together.