Cut the lemons in half and squeeze out all the juice from the pulp.

Pour the sugar and cornstarch into the lemon juice and whisk until the ingredients are completely dissolved.

Pour the lemon juice mixture into a saucepan and cook over low heat until it thickens, stirring constantly.

Transfer the thickened lemon mixture to a separate bowl and place it in the refrigerator to chill.

Meanwhile, whip the cold heavy cream with a mixer until it thickens and holds soft peaks.

Beat the chilled lemon mixture until it turns pale, then gradually add it to the whipped cream, mixing with the mixer as you go.

Transfer the cream to a piping bag. You can use a piping tip to create pretty swirls in dessert glasses or cups. Decorate as desired.