The topic of the paragraph is about a new kind of pie called slab pie. The author is saying that slab pies are taking over summer dessert tables because they are easy to cook and carry yet still able to satisfy a crowd. Slab pies are made by doubling or tripling standard crust and filling recipes, then baking them in a large rimmed cookie sheet. A single pan full is easy to cook and carry yet still able to satisfy a crowd. Easily cut into squares, slab pies also have a slightly thicker crust so they can be served and even hand-held without fuss. The stated main idea is that slab pies are becoming popular at big parties because they are easy to cook and carry yet still able to satisfy a crowd.