Juicy plums are excellent for eating out of hand, but baking with them is one of the finest pleasures of summer. Their flesh is sweet and their skins are tart, so they inspire use in tarts, crumbles, muffins, coffee cakes – or in this case, an easy walnut cake. The walnuts also give moistness and earthy flavor to the cake, which is heavily scented with the zest of an entire lemon. The whole dough can be made in a few minutes in the food processor. Bonus points: You don’t even have to peel the plums! You can use any kind of plum you like in this recipe. When I shopped for this cake, I bought two different kinds of plums and was surprised to see that the colors inside each of them were so different. Color coordination just doesn’t matter, because the end result is a cake that is gorgeous no matter what, and even better to eat. As the season goes on, make sure to try this cake with other fruits like apples, pears, or late-season peaches. Heck, even cranberries would be a great choice for this easy cake. Bring this cake along on a picnic, to a potluck, or just share it with your family for a special weeknight treat. Generously butter a 10-inch ovenproof skillet with a heatproof handle or a 9-inch cake pan. Halve, pit, and thinly slice the plums. Add the eggs one at a time, and process after each addition, until fluffy. Add the lemon zest, vanilla, flour, baking powder and salt, and pulse just until the batter is smooth. Finally, add the ground walnuts and pulse to mix them into the batter. The batter will be thick. Lay slices of plums in a ring around the outside edge of the pan, overlapping the slices slightly. Arrange a second ring of slices inside the first, and then fill in the very middle of the cake with the remaining slices. Sprinkle with the turbinado sugar. Set the skillet on a wire rack to cool to room temperature.
