Melt 1 T of the butter in the microwave (be sure to cover). Stir cookie crumbs into butter. Press mixture into bottoms of 2 oven-safe ramekins.
In a small (cold) saucepan, whisk together the lemon juice and zest, water, 1/4 c sugar and cornstarch.
Place saucepan over medium heat and cook, whisking constantly, until mixture is thick and gooey, like wallpaper paste.
Stir in remaining 1 T butter followed by egg yolk.
When lemon custards are fully cooled, combine egg white and 1 T superfine sugar in a deep mixing bowl. Beat with an electric mixer starting at low speed and increasing gradually until soft waves are formed and sugar is dissolved.