Posset is a very old dish, although it has transformed over the centuries from a kind of curdled drink made from wine and cream (yuck!) into a delicious dessert of cream and lemon juice. It has become very fashionable lately, and it's really easy to make.
Remove the zest from the lemons and squeeze 100ml (3.5 fl. oz.) juice into a small saucepan. It's important to measure the lemon juice as too much or too little can affect the setting of the posset. Add the caster sugar and heat gently until the sugar has dissolved and you have a syrup. While this is going on, heat the cream and most of the lemon zest in another pan until almost boiling. Pour the cream over the syrup, mix well, and then strain into a jug to remove the zest. Pour into 3-4 tumblers or ramekins and put in the fridge to set. This will take at least 2 hours.
When the posset has set, chop the almonds and lightly toast them in a dry frying pan. When they are cool, sprinkle a few onto each posset, along with a few shreds of lemon zest.