Line a sieve with clean muslin or a clean Chux cloth and place over a bowl. Spoon the yoghurt into the lined sieve. Cover and place in the fridge for 1 hour or up to 8 hours if time permits (see tip).
Combine the strawberries, raspberries, blueberries, blackberries (if using) and sugar in a bowl, stir gently to combine. Stand for 15 minutes at room temperature.
Heat a large non-stick frying pan over high heat until hot. Add the berries and any undissolved sugar in the bowl. Cook, gently shaking the pan for 1 minute. Remove the pan from the heat and allow the berries to cool to room temperature (see tip).
Meanwhile, combine the maple syrup and cinnamon in a small saucepan. Bring to a gentle boil, stirring often. Boil gently for 1 minute until the maple thickens slightly. Pour into a heatproof bowl and set aside to cool.
Spoon the thick yoghurt from the sieve into a bowl, discarding the drained liquid. Stir in the cinnamon maple mixture then thickly spread over the toasted sourdough. Spoon over the berries and syrup and serve.
TipTip The longer you hang the yoghurt the thicker it will be. It will keep 7 days in the fridge in a clean airtight container.
TipTip The berries (step 2-3) can be made ahead and spooned into a clean jar or airtight container. They will keep for 5 days in the fridge.
TipTip The berries are delicious over your breakfast cereal or a bowl of yoghurt for lunch, as a snack or dessert.