To a heavy-bottomed skillet or pan, set over medium heat, add the sugar, butter and walnuts. Stir occasionally until the sugar begins to melt, then stir constantly as the sugar begins to caramelize and the nuts become toasted, about 5-6 minutes. Be quick as it will burn in a heartbeat if you are not careful. Remove from the heat and transfer the nuts to the prepared parchment paper. Using two dinner forks, quickly separate any nuts that are stuck together. While the nuts are still hot and sticky sprinkle them with the kosher salt. Allow to cool, then transfer to a dish until ready to use.

Add the vinegar, garlic, salt, pepper and honey to a small dish or blender. Whisk or blend to fully combine. Slowly drizzle in the olive oil while continuing to whisk, or if using the blender while the motor is running. The vinaigrette will emulsify and become thick and creamy. Transfer to a small pitcher.

In a large salad bowl, toss the salad greens, blackberries, feta cheese and onion slices with just enough of the vinaigrette to moisten the greens. Top with the glazed walnuts and serve.

Alternatively, toss the salad greens, blackberries, feta cheese and onion slices together, divide into 4 chilled salad plates, top with glazed walnuts and pass the pitcher of vinaigrette to guests.