Mix rolled oats, sugar and salt in a mixing bowl.
Cut butter into small pieces and add to the oat mixture.
Quickly knead the oat mixture into a dough, adding a little water as needed.
Divide the dough into two equal pieces.
Roll out each piece of dough between two sheets of baking paper, each about 4 - 5 mm thick, to form two rectangles of equal size.
Place the two oatmeal bases side by side together with the baking paper on a baking tray.
Refrigerate the baking tray with the oatmeal bases for 1 hour.
Remove the top sheets of baking paper, bake the two oatmeal bases in a preheated oven at 392 °F (200 °C) for about 15 minutes and let them cool to warm on the baking tray.
Carefully spread one of the oatmeal bases with jam, turn the second oatmeal base on top and let the oatmeal cake cool completely.
Cut the oatmeal cake into bars.