Place the butter, sugar, lemon zest and juice in a large bowl and microwave on full power for about 2 minutes or until the butter and sugar has dissolved (or use the top of a double boiler or bowl over a pan of hot water).
Add beaten eggs and continue cooking in 1 minute bursts, stirring each time. Reduce to 30 second burst as the mixture thickens. It is ready once the mixture is thick enough to coat the back of the spoon.
Strain through a sieve into the wide necked jug. Pour into cooled sterilized jugs and cover with a wax disc or cellophane or a screw on lid.