Put the cream and granulated allulose in a medium saucepan. Heat over a low heat, stirring regularly until the sweetener has dissolved (**see notes). Let the mixture bubble gently for 2-3 minutes while stirring often.
Turn off the heat and add the lemon juice and zest. Stir to combine.
Pour the posset into 6-8 small dessert bowls or shot glasses. Cool to room temperature, then cover and chill in the fridge for at least 3 hours or overnight.
