In a bowl, knead the ingredients into a smooth dough and shape it into a large ball.
Cover it with foil and let it rest in the fridge for at least 30 minutes.
Preheat the oven to 170°C.
Roll out the dough to a thickness of 4-5 mm on a lightly floured board.
Cut out shapes or circles with small cookie cutters. Knead the remaining dough again, then roll it out again and cut out more cookies. When the dough is completely used up, you can stamp out the centre of half of them, depending on the pattern (e.g. flower, heart)
Arrange the cookies on a baking sheet, lined with parchment paper.
Bake for about 12-15 minutes until light brown. It is important that they should remain very light, because if you over-bake them, the texture of the cookies will be dry and too flaky.
Leave them to cool on the baking sheet.
When they have cooled completely, spread jam on the base cookies then top with the cut-out cookies, pressing them together.
Dip the sandwich cookies in powdered sugar, if liked.
The cookies can be stored in an airtight container for about 3 days.