Make the dressing: Add the raspberries, oil, honey, vinegar, red onion and salt to a blender and blend on high until smooth. Stir in the poppy seeds.
Prepare the kale: Add the chopped kale to a large bowl with a sprinkle of salt. Massage the kale with your fingers until tender and slightly wilted.
Assemble the salad: Add the kale, berries, clementines, cashews and feta to a large serving bowl. Drizzle on some of the dressing and gently toss to combine. Add more dressing, if desired.
Notes
Massage kale. As curly kale is tough and chewy, you need to massage it before adding it to a salad to make it tender.
Use a blender. To achieve a smooth and emulsified texture for the dressing, you'll need to use a blender. I just use the small smoothie cup blender I have, but you can also use a full size blender.
Gently toss together. Raspberries can be a bit delicate, so once I add the dressing, I toss everything together carefully as to not break apart the raspberries.
Extra dressing. I prefer to have too much dressing than not enough, so the recipe makes a lot. Just use as much as you like, and store the rest in the fridge for another salad.