Preheat the oven to 160°C / 320°F / Gas Mark 3.
Beat together the margarine and sugar until fluffy (for at least a minute), then add the rice flour and salt, and beat again.
Add the plain flour, and mix slowly until just combined into a crumbly dough. (It won't really hold together at this stage, but don't panic!).
Cover two baking trays with baking parchment or greaseproof paper. Roll out the dough to around the thickness of a £1 coin. Use a star shaped cutter to cut out as many biscuits as you can, placing them on the baking trays. Then roll the offcuts together and re-roll and cut again. Continue until all the dough has been used up. Then use a smaller star shaped cutter to cut 'windows' out of half the biscuits, and carefully remove the centres.
Sprinkle a little caster sugar over the 'window' biscuits, and press it gently into the dough. Bake in the oven for 10-12 minutes, with the whole stars on the upper shelf and the 'window' stars on the lower shelf. Don't let them brown - they should stay fairly pale, you can check the bottom of the whole stars to make sure they are cooked through. Remove and place on a cooling rack.
When the biscuits are completely cool, spoon around 1 tsp jam onto each of the whole stars and spread near to the edges with a knife. Place one of the window stars on top and dust with a little icing sugar if you wish.