Sweet cheese is made with farmer's cheese, which is like a dry ricotta or mascarpone, with a touch of added sugar and maybe vanilla depending on who's making it. The result is a slightly sweet, crumbly-textured cheese filling that makes for a pretty versatile pierogi. My husband and I both like them plain, just sauteed in butter, but the kids like them as a dessert with a fruit-syrup drizzle and a dusting of confectioner's sugar. Or you can go all out in the dessert vein and make fruit-and-sweet cheese filling that turns out something like a cheesecake pierogi.