Set out 4 small ramekins or serving glasses on a tray that will fit in your refrigerator.

In a medium saucepan, combine the heavy cream and sugar. Heat over medium heat, stirring occasionally, until the mixture comes to a full boil. Let it boil for 2-3 minutes, stirring constantly to prevent scorching.

Remove the pan from heat and immediately stir in the fresh lemon juice, lemon zest, and a pinch of salt if using. Whisk well to combine. The mixture will thicken slightly as the acid reacts with the cream.

Pour the mixture through a fine-mesh strainer into a measuring cup or bowl with a spout to remove any zest pieces and ensure a silky smooth texture.

Carefully divide the lemon posset mixture evenly among the prepared ramekins or glasses, pouring slowly to avoid bubbles.

Cover each ramekin with plastic wrap and refrigerate for at least 3-4 hours, or preferably overnight, until the possets are completely set and firm.

Remove from refrigerator 10 minutes before serving. Garnish with fresh mint sprigs, additional lemon zest, or fresh berries if desired. Serve chilled.