When it comes to baking, this one-bowl skillet cake is as easy as it gets. Martha made this recipe on Martha Bakes episode 609.
Preheat oven to 350 degrees. In a 12-inch enameled cast-iron skillet or ovenproof baking dish, melt butter in the oven, 5 to 7 minutes.
Whisk together flour, sugar, baking powder, and salt in a large bowl. Remove skillet from oven and add melted butter to flour mixture; stir to combine. Add milk and vanilla extract; mix until well combined. Pour mixture into skillet and arrange plums evenly on top, leaving a 1-inch border.
Transfer skillet to oven and bake until top is golden brown and a cake tester inserted into the center comes out clean, about 1 hour. Let cool slightly on a wire rack. Serve hot, warm, or at room temperature with whipped cream, creme fraiche, or ice cream.