• Preheat oven to 350°F / 180°C / Gas mark 4.

Make the filling

• Whisk egg yolks and lime zest together in a medium bowl. (After 1 1/2 - 2 minutes, your mixture should have yellow - green tint from the lime zest.)
• Whisk in condensed milk until mixture is smooth, then whisk in lime juice. Cover and set aside.

Make the crust

• Put graham crackers in food processor and run for about 45 seconds until you have fine crumbs. 
• Pour melted butter over crumbs, then add sugar and salt. Pulse (5 -7 times should do) until you have what resembles wet sand.
• Pour crumbs into pie plate, pressing crumbs into an even layer on bottom and sides.  *Using the bottom of measuring cup makes this task much easier!
• Bake crust for 10 - 12 minutes then remove from oven and set on wire rack. 

Assemble the pie

• Pour filling into warm pie crust and bake 15 - 18 minutes.
• Remove from oven and let the tart cool for 30 - 60 minutes before refrigerating. 

  Once cooled, place in refrigerator for 2 - 3 hours until chilled and set.
• Top with freshly whipped cream, if desired.

Whipped cream

• *About 30 minutes before you plan to make whipped cream, place the mixing bowl and the beaters in the refrigerator. It will whip up faster if everything is cold.

  Add whipping cream, powdered sugar and vanilla extract to the chilled bowl. Using a hand held electric mixer, whip the ingredients together, starting on low speed and increasing to high slowly as it begins to stiffen up.
• Beat for 60-90 seconds until stiff peaks form. About halfway through, stop to scrape down the sides of the bowl.

  Transfer to a piping bag, or dollop on top of the pie. Serve immediately.