Prepare the Fruit : Gently rinse and pat dry the strawberries and blackberries. On your cutting board, hull and quarter the strawberries and slice any particularly large blackberries in half. Set aside.
Create the Creamy Base : In the basin of a high-speed blender, combine the low-sodium cottage cheese and fresh lemon zest. Secure the lid and process on high for 75 to 90 seconds, using a spatula to scrape down the sides halfway through. Continue blending until the mixture is completely smooth, airy, and has a texture similar to ricotta.
Toast the Sourdough : Place the large cast-iron skillet over medium heat. Arrange the sourdough slices in a single layer (working in batches if necessary) and toast for 2–3 minutes per side. The bread is ready when it's an even golden-brown and feels crisp to the touch.
Build the Toasts : Transfer the warm toasted bread to serving plates. Generously spread a layer of the whipped cottage cheese mixture, about ¼ cup per slice, across the surface of each piece of toast.
Arrange the Berries : Artfully distribute the prepared strawberries and blackberries over the whipped cottage cheese, creating an even mix of color and texture on each toast.
Final Touches : Drizzle each toast with a ribbon of agave nectar or maple syrup. Garnish with a few fresh mint leaves just before serving for a pop of color and fresh aroma.