Use graham or arrowroot crumbs. No quince jelly? Use crabapple or another tart red- or orange-hued jelly. No mascarpone? Use labneh, which will make the cake a little tarter and a little less rich.
The quince tree ( Cydonia oblonga) is in the rose family along with apples and pears, but is the only member in the Cydonia group. The fruit is tough to cut, and the cut flesh is the color of an apple ...