Preheat the oven to 300°F (150°C). Line your 9×5-inch (23x13cm) loaf pan with parchment paper, leaving an overhang.
In a blender or food processor, blend the cottage cheese until completely smooth.
Add Greek yogurt.
Add eggs, honey or maple syrup, vanilla extract, and a pinch of salt.
Blend until smooth and creamy.
Add cocoa powder and cornstarch.
Blend again until fully incorporated and the batter is thick but pourable.
Transfer about 1¼ cup (300 g) of the batter to a small bowl.
Add two tablespoons of cocoa powder.
Mix, to create a darker chocolate portion.
Pour the remaining (lighter) batter into the prepared loaf pan.
Drop spoonfuls of the darker batter on top.
Use a skewer or knife to gently swirl in loose, figure-eight motions. Don’t overmix; distinct swirls should remain.
Cover loosely with foil and bake for 50–60 minutes, until the edges are set and the center is slightly jiggly.
Let cool at room temperature for about 30 minutes, then refrigerate for at least 4–6 hours or overnight to fully set.
Carefully lift out using parchment, slice with a hot knife, and serve.
Serve as is or top with fresh berries for a bright contrast.