Generously butter an 8-inch springform pan. Add a parchment round to the bottom and butter that, too. If using a regular pan, lightly flour the pan as well.
Spoon mixture into prepared baking pan. It will be quite thick — use an offset spatula to spread the batter out. Starting on the outer edge and working your way in, tuck the sliced fruit into the cake batter, taking care to press each slice lightly in. If using berries or cherries, scatter the fruit over top and gently press it into the top. Bake cake for 45 - 55 minutes, until the edges are golden and just pulling away from the edge of the pan and a toothpick inserted in the center comes out with just a few crumbs attached.
Cool 30 minutes. Run a knife along the edge and open the spring form. Let the cake cool completely. If cake was baked in a regular pan, let it cool completely before running a knife along the edge, flipping it out onto a plate, and then quickly re-flipping so the cake is right side up.