Sponge Cake and Lekach

Marble cake, sponge cake, or the like, which is a liquid batter before baking, can only have hafrasha done after baking, assuming it has the minimum shiur of flour (תורת הארץ ). Often, the cake is mostly oil, eggs, sugar, and other ingredients, and the flour is the minority, in which case it is potur from challah (שו"ת מנח"י ח"ח סי' ק"ט ).