Do foamed eggs whites, folded into a batter including some liquid, contribute to the thickening of that liquid?
A class of English 'puddings' are those derived from 'lemon surprise pudding'. In these baked puddings a sponge forms on top and a flavored custard below.
Butter is creamed with sugar, egg yolks beaten in and a liquid (normally dairy), a small amount of flour and then also flavored liquid, e.g. lemon juice, orange juice, puréed fruit etc. Finally, foamed eggs whites are folded in.
In deciding the quantity of eggs required to thicken the liquid, should I consider the egg whites, or do the egg whites solely provide leavening/rising potential? Should I just consider the thickening power of the yolks?