Preheat your oven to 180°C (160°C fan) or Gas Mark 4. Grease two small ramekins or a small baking dish with a little butter or oil. You'll know the oven is ready when the heating element glows orange and you feel a steady warmth when opening the door.

In a blender, combine the rolled oats, banana, egg, milk, maple syrup, baking powder, cinnamon, vanilla, and salt. Blend on high for 45 seconds to 1 minute. The mixture should be completely smooth, with no visible oat flakes, and have a thick, pourable consistency similar to pancake batter. It will smell sweet and slightly of banana.

Pour the batter into your prepared dish or ramekins. If you're adding chocolate chips or berries, gently fold them in now with a spatula. The batter should fill the dish about two-thirds full, leaving room for it to rise.

Bake for 20-25 minutes. The top will turn a lovely golden brown, and the edges will start to pull away from the sides of the dish. You'll know it's done when you gently press the centre and it springs back, and a skewer inserted into the middle comes out clean. Your kitchen will smell like a warm bakery.

Remove from the oven and let it cool in the dish for 2-3 minutes. The surface will settle slightly, and the steam will stop rising. This short rest helps the structure set so it doesn't collapse when you serve it.

Serve warm. You can eat it straight from the ramekin with a spoon, or turn it out onto a plate. It should be tender and fluffy, with a slightly crisp top edge if baked in a shallow dish.