Prepare pancakes following the classic recipe - see 'Goes well with'. Fold the pancakes into quarters.
Tip the caster sugar into a non-stick frying pan and set the pan over a low-medium heat. Allow the sugar to melt slowly without stirring and continue to cook until it becomes a deep amber-coloured caramel.
Immediately slide the pan off the heat and add the orange juice - be careful as it may splatter and spit as it hits the hot caramel. Add the orange zest, lemon juice, the Grand Marnier and return the pan to a low heat to re-melt the caramel into the liquid.
Add the butter to the sauce in small pieces, bring to the boil and simmer gently until glossy and reduced slightly. Add the pancakes to the pan and warm through. Serve immediately.