This moist blueberry traybake cake can be made with fresh or frozen blueberries and is a great choice when you're serving lots of people.
You can make your own vanilla sugar by sticking scraped-out vanilla pods into a jar of sugar and waiting a couple of weeks. I just add any used vanilla pods to the jar. Or you can leave it out. In that case just add a couple of teaspoons more sugar and a bit of vanilla extract.