1. Place the jam or marmalade and 150 ml (A pint) water in an ovenproof glass bowl and microwave on HIGH for 2 minutes.
2. Blend the arrowroot or cornflour with 30 ml (2 tbsp) water until smooth and then stir it into the heated mixture.
3. Microwave on HIGH for 1-2 minutes or until boiling, stirring after 1 minute.
4. Add lemon juice to taste, and sieve if preferred before serving.