Grease a 10-inch deep-dish pie plate or soufflé dish. Prepare the apples and rhubarb and arrange in the bottom of the pan. Using a blender or a bowl with a whisk, combine the eggs, maple syrup, yogurt, vanilla and cinnamon. Pour the custard over the fruit. Bake around 45 minutes, until it just sets. Let cool on a rack and enjoy at room temperature.