This old-fashioned crumble is homey, perhaps nostalgic, and incredibly easy to make. Serve it warm or at room temperature, on its own or with vanilla ice cream. This probably goes without saying, but it also makes a delicious breakfast the following day. Olallieberries are found at the farmers’ markets in California in the summer months, but you can substitute blackberries, raspberries, strawberries, blueberries, or a combination of your choosing.