- Preheat the oven to 190°C/375°F/gas 5.
- Put the apple slices into a pan with granulated sugar and water.
- Cook over a low heat for 5 minutes and place in a small ovenproof dish.
- Place the flour and oats in a bowl, mix well. Cut butter into small cubes and add it the oats and flour.
- Mix with your fingertips until it resembles an even crumby texture. Add powdered sugar and mix through.
- Cover the fruit with this crumby mixture. Bake for approximately 20 minutes until the crumb is golden.
- Serve immediately.