1: Beat together the yolks of 3 eggs with 140 g caster sugar until the mixture foams and turns white.
2: Add the egg whites a little at a time...
3: ...allowing the mixture to "foam" each time before adding more.
4: At the end, add the red colouring.
5: Sieve 125 g flour onto the mixture and fold in gently with a soft spatula. Lean the bowl over on its side to do this more easily.
6: Preheat the oven to 360°F (180°C). Reims biscuits are normally rectangular, but you can use whatever shape moulds or tins you have available. Fill the moulds 3/4 full.
7: Dust with icing sugar and bake for about 20 minutes.