Preheat the oven to 325 F.
Fill one-third of a medium sized pot with water.
Bring the water to a simmer.
In a medium bowl add in the zest and juice.
Next, whisk in the eggs.
Add the sugar and butter (if using)
Place the bowl on top of the simmering water.
Whisk until the sugar and butter are melted and the mixture is smooth.
Remove from the heat, strain out and allow to cool.
Place the lemon filling inside the ChocolateTart.
Bake in the oven for about 8 to 10 minutes.
Cool the tart completely.
Garnish with fresh fruit.
