If making the strawberry lemonade variation, blend the strawberries and finely strain them. You will need about ½ cup of strawberry juice for this recipe.
Cut the lemons in half widthwise. Using a spoon or small knife, carefully scoop out the flesh and juice, being careful not to puncture the rind.
Save the inside flesh of the lemon, squeeze out the juices and strain into a bowl or cup and set it aside for the filling. You will need 6 tbsp of reserved lemon juice for the filling.
Set the halved lemon cups onto a tray or use a muffin tin to set them in so they are sitting upright and are stable for easing transfer into the fridge.
In a medium saucepan over medium heat, combine the heavy cream, sugar, and lemon zest (if using). Stir and bring to a gentle simmer. Do NOT let the cream boil.
Let it bubble lightly for 3 minutes, stirring frequently.
Remove the pan from the heat and let it cool for 1-2 minutes. Then, slowly mix in the 6 tbsp of the reserved lemon juice.
Carefully pour the warm posset into the prepared lemon cups. Let them cool at room temperature for about 30 minutes, then refrigerate for at least 2.5-3 hours or until fully set.
Before serving, you can garnish with sanding sugar and a berry if desired.
