Combine the graham cracker crumbs and melted butter in a bowl until the mixture resembles wet sand.

Press the crumb mixture firmly into the bottom of a 9x13-inch dish to form an even crust.

Dissolve the lemon gelatin in boiling water, stirring until completely smooth. Mix in the sugar, lemon juice, and salt.

Refrigerate the gelatin mixture for about 20 minutes until slightly thickened but still pourable like thin syrup.

Pour the chilled evaporated milk into a cold mixing bowl and beat with a hand mixer until soft peaks form and the volume increases.

Gently fold the thickened gelatin mixture into the whipped milk until fully combined and fluffy.

Spoon the filling over the prepared crust and spread it into an even layer.

Cover the dish and refrigerate for at least 2 hours, or until the filling is firm and slices hold their shape.

Cut into squares and serve chilled with whipped cream if desired.