Preheat the oven to 1750C. Mix butter with the cracker crumbs, sugar and salt in a bowl. Press the mixture into the bottom and up the sides of the prepared pan. Bake until golden brown, about 15 minutes. Cool completely on a rack.
Chop the avocados in a bowl, add the cream cheese and beat with a mixer on medium speed until smooth.
Add MILKMAID, lemon juices, and the salt and beat until fluffy. Fold the gelatin and mix well. Pour the filling into the crust, cover the surface and chill at least 4 hours.
Garnish with whipped cream, if desired, and serve immediately (the top will start to brown as the pie sits).