Add California Blueberries, sugar, and water to a small saucepan. Bring to a simmer over medium heat, stirring occasionally, until the berries burst and the mixture thickens slightly, 8–10 minutes. Lightly mash the berries, then strain through a fine mesh sieve. Add lemon juice and let cool completely.
In a small bowl or jar, combine cold heavy cream, blueberry syrup, cardamom, and salt. Whisk or froth until thickened but still pourable (soft, cloud-like consistency).
Sift matcha into a bowl to remove any clumps. Add 2 tbsp warm water and whisk into a smooth paste. Add remaining water and whisk vigorously in a zig-zag motion until frothy.
To assemble, pour matcha into a glass (add ice if you like), then gently pour the blueberry foam over the top. Finish with a matcha powder.