Don’t roll it too thin as it needs to be robust enough for the filling and meringue. For the pastry ... until it has the consistency of a thick custard. Remove from the heat and cool slightly.
Remove from the heat and whisk in the lemon juice and zest and the butter. Set aside. Stir a pinch of cream of tartar into a half-cup (and 2 Tbsp) sugar. Set aside. Whisk the egg whites until ...