Pour the condensed milk and vanilla into a mixing bowl. Add the lemon zest and mix well to combine.

Whip the cream until stiff peaks form. Fold 1 cup of whipped cream into the condensed milk mixture. Add the rest of the cream and fold in lightly to combine. Pour the mixture into a baking paper-lined loaf tin and smooth out the top.

Add a little more lemon zest to the top, then cover with a sheet of baking paper and lightly press it into the mixture so that there is no air between the mixture and the paper. Place into the freezer overnight to set.

To serve, remove the ice cream from the freezer and allow to stand at room temperature for 8-10 minutes to soften slightly, then scoop and serve.