Line a 9x13-inch baking sheet with parchment paper, letting the edges hang over for easy removal later.
Place white chocolate in a microwave-safe bowl. Microwave in 30-second intervals at 50% power, stirring after each interval, until completely melted and smooth (about 2-3 minutes total).
Pour the melted chocolate onto the prepared baking sheet and spread it into an even layer about 1/4-inch thick using an offset spatula or the back of a spoon.
Tap the baking sheet firmly on the counter 3-4 times to release any air bubbles and create a smooth surface.
Immediately arrange the sliced strawberries and blueberries over the chocolate in a random or patterned design, pressing them gently into the surface.
Refrigerate for 30 minutes or until the chocolate is completely set and firm to the touch.
Remove from the pan using the parchment paper overhang, then break or cut into irregular pieces or neat squares using a sharp knife.
