If you have a sweet tooth, you must check this place out:
Pastelerķa San Antonio
There isn't anything particularly "Peruvian" on the menu, aside from alfajores, but the array and quality of cakes, pastries, etc. is staggering.
It's on the edge of Miraflores, not too far from Larcomar.
[Addendum: According to the website, there is also a location in San Isidro]