01 - Combine the mixed berries, water, and salt in a medium saucepan. Bring to a gentle boil over medium heat.
02 - Reduce heat and simmer for 5 minutes, until berries are softened and release their juices.
03 - Using an immersion blender, purée the soup until smooth. If using a countertop blender, carefully transfer the hot soup and blend, then return to the saucepan.
04 - Stir in the coconut milk, maple syrup, lemon juice, and vanilla extract until well combined.
05 - Bring back to a low simmer. Slowly whisk in the cornstarch slurry while stirring constantly. Cook for 2–3 minutes until the soup slightly thickens.
06 - Remove from heat and allow the soup to cool to room temperature, approximately 30 minutes.
07 - Refrigerate for at least 1 hour until thoroughly chilled. Serve cold, garnished with reserved sliced strawberries and additional fresh berries if desired.