To prepare crust, preheat oven to 350°F/180°C. Lightly butter a 9-in. pie pan.
In a mixing bowl, combine crumbs, sugar and butter. Transfer crumb mixture to pie pan and firmly press mixture into bottom and up the sides of pie pan. Bake for 8 - 10 minutes and cool before filling.
To prepare the filling, bring about 2 inches of water to a simmer in a large saucepan. Meanwhile, place egg yolks in a heatproof bowl (that will fit into the saucepan, but not touch the water) and whisk until smooth.
Gradually whisk in the sugar and beat until mixture is creamy. Add salt, zest and juices and mix until smooth.
Place bowl over the simmering water and whisk mixture by hand until it is very thick, about 10 - 15 minutes. The mixture should coat the back of a spoon.
Carefully remove bowl from heat. Whisk in butter and continue to stir until butter is fully incorporated. Strain filling, cover and chill until cold, about 1 hour.
Pour heavy cream into a small bowl or large measuring cup; using an immersion blender with a whisk attachment, beat cream on low speed for about 20 seconds or until fully whipped.
Fold cream into cooled lemon filling and spoon mixture into prepared piecrust.
To prepare the meringue, preheat oven to 375°F/190°C. Add egg whites and salt to a small bowl or large measuring cup and using the whisk attachment, beat egg whites on medium speed until foamy.
Add confectioners’ sugar and beat on low speed for 1 minute.
Transfer egg mixture to a large bowl. Using low speed, gradually add granulated sugar; add vanilla. Increase speed to high and beat for 3 minutes or until appropriate consistency is reached. The meringue should be very thick and hold a firm peak. Either pipe or spread meringue over lemon filling.
Bake pie on middle rack of oven for 8 - 12 minutes or until meringue is golden brown.
Transfer pie to a wire rack and cool completely. Chill pie for 2 hours before serving. This pie is best served the day it is prepared.