LEMON CURD:

Using a grater or a carrot peeler, remove the zest of 3 lemons, being careful to avoid the white pitch. Put the zest in a food processor fitted with steel blade. Add the sugar and pulse until the zest is finely minced into the sugar.

Cream the butter and beat in the sugar and lemon mixture. Add the eggs, one at a time, and then add the lemon juice and salt. Mix until combined.

Pour the mixture into two quarts saucepan and cook over low heat until thickened (10 to 20 minutes). The lemon Curd will thicken about 170°F Fahrenheit, or just below simmer. Remove from the heat, cool and then refrigerate.

ICE CREAM:

Place the sugar, milk, vanilla extract, and half a cup of the heavy cream in a medium pot. Warm the mixture, stirring occasionally. Once the mixture has warmed, remove from heat and cool for a few minutes.

Whisk the egg yolks together in a medium bowl. Pour the milk and sugar mixture slowly into the egg yolks, whisking constantly to avoid scrambled eggs.

Pour the egg yolk and milk mixture back into the medium pot, and place over medium heat. Add the salt at this point. Use a wooden or rubber spatula to stir constantly, and make sure to scrape along the bottom of the pan. Be careful of over cooking. The mixture is ready when it has a custard-like consistency and coats the spatula.

Prepare an ice bath with a large bowl inside it, containing the remainder of the heavy cream. Pour the egg yolk and milk mixture into the bowl with the heavy cream. Keep mixing until the mixture has cooled. Pulverize the graham crackers and add them to mixture at this point. Whisk well together.

If the mixture is chilled you can run it through an ice cream maker, if it is not chilled, put the mixture in the fridge for a couple of hours before proceeding with the ice cream maker. Follow the manufacturer's direction to prepare the ice cream. in the last five minutes add the lemon Curd. After finish, remove the ice cream from the ice cream maker with a spatula and place it in an airtight container and this in the freezer for at least two hours.

OPTIONAL: if you don't have an ice cream maker you can make the ice cream by hand. After step 9 pour the mixture in a airtight container and this in the freezer. Every 30 minutes remove the container from the freezer and whisk the mixture thoroughly (this is to avoid ice crystals). Keep doing this every half an hour for the next 4 hours. In the second to last whisk, add the lemon Curd.