Rinse the spinach and remove the stems. Thinly slice the red onions and soak in cold water. Rinse the raspberries and strain well.
For the caramelized walnuts, you need to make caramel, once it is light brown, add the nuts and stir well until they are completely caramelized.
Mix the apple cider vinegar, olive oil, salt, and pepper for the dressing.
To assemble the salad, first arrange the spinach base, the onion slices, spread the ricotta, caramelized walnuts, and finally the raspberries.