For the candied nuts: In a nonstick skillet over medium-high heat, toast the pistachios and hazelnuts until fragrant, 4 to 5 minutes. Add the brown sugar, salt, vanilla and 1 tablespoon water directly to the pan with the nuts and stir to coat them. Cook until the sugar has dissolved, about 1 additional minute. Transfer to a parchment-lined baking sheet and allow to cool, 12 to 15 minutes.
For the dressing: Combine the olive oil, vinegar, maple syrup, mustard, salt and pepper in a mason jar. Secure the lid and shake to combine. Set aside.
For the salad: Spread the arugula, kale and spinach over a large round platter, leaving space in the center of the platter (it should look like a holiday wreath). Top the greens with the radicchio. Arrange the mandarin segments over the greens. Sprinkle with the pomegranate seeds, cranberries, blueberries and cooled candied nuts.
Lastly, sprinkle with the Parmesan, creating the look of snow. Shake the dressing one more time and pour it into a serving bowl. Place the bowl in the center of the platter and serve.