Beat the butter and sugars together until light and creamy, then beat in the egg, vanilla and lemon again until light and creamy.
Gently mix through the flour and salt until completely combined - do not overmix.
Pat the dough out into an even rectangle on the lined baking sheet - it should be about ½ inch thick - then place in the refrigerator for about 30 minutes. Meanwhile, preheat the oven to 180C/350F.
Using a 3 inch circle cutter, mark out as many cookies as you can from the rectangle of dough, and use the back of a tbsp to make indents in each circle. Fill the indents with jam, and then bake the cookie for 35-40 minutes, or until dark golden brown.
When the cookies have just come out of the oven, use the same circle cutter to cut out each cookie completely, and then leave to cool on the tray.
When cool, break up the surrounding extra cookie to release the shortbreads (keep it to nibble on or make biscuit bases with) and then eat!
Recipe by The Sugar Hit at https://www.thesugarhit.com/2015/08/giant-brown-sugar-jam-shortbreads.html