Trim the stems off of the strawberries and add them to a blender with the raspberries, milk, maple syrup and vanilla extract. Blend together until smooth.
Add the chia seeds to a small baking dish or container and pour in the strawberry milk and a pinch of salt. Whisk together well.
Cover the dish and refrigerate overnight or for at least 4 hours. Once chilled, mix again to break up any chia clumps.
Top with yogurt, nuts, crushed freeze-fried berries or fresh fruit.