Step 1 - Pour the lemon juice into a saucepan with the chopped pears, marsala and vanilla paste. Put over a moderate heat, cover and simmer until the pears are soft. This may take about 20 minutes. Puree the pears by passing them through a sieve.
Step 2 - Pour the cream into a saucepan and bring to the boil and then set to the side.
Step 3 - Whisk the egg yolks and sugar until creamed together. Gradually stir in the hot cream and then return to the hob over a low heat.
Step 4 - Stir continuously with a wooden spoon until it forms a thick custard.
Step 5 - Add the custard to the pear puree and allow to cool completely before chilling it in the fridge.
Step 6 - Once chilled, the ice cream can be added to an ice cream maker and processed as per the instructions for your specific ice cream maker. If you are not using an ice cream maker then put the chilled ice cream into a tupperware box and stir it up every 40 minutes or so. This process should be repeated until the mixture has frozen into a smooth, soft-set ice cream.