I take it yer making the cake as if it were a vector/or nor doesn't matter.
I'd use a texture-- a white stucco wall or a painted wall would be perfect--
over each layer I'd set it to "soft light" and decrease opacity a bit...
alt+clik on line between the two layers and done...
easy squeezy lemon pleezy looks real.
*edit*..take my advice on this one.

u dont have to choose one or another teqhnique ,SS technique should be great too... i just wanted to help with the allsource style...not more (well 1 hour to make the screenshots and the chop tho)