Preheat an oven to 400 degrees. Spray a large baking sheet with cooking spray and place sweet potato wedges on top. Toss the sweet potatoes with ginger, olive oil, kosher salt and pepper. Roast the sweet potatoes for about 45 minutes tossing midway through.
While the sweet potatoes are cooking, make the pickled walnut salsa. In a medium saucepan combine white wine vinegar, granulated sugar, and ½ tsp kosher salt. Bring the mixture to a boil and add 3/4 cup walnuts. Remove the saucepan from the heat and stand until completely cool.
Once the walnuts have cooled, drain them. Next place the remaining 3/4 cup walnuts, olive oil, roasted walnuts, tarragon and lemon juice in a bowl. Toss to combine.
Next, make the blue cheese dressing. In a medium bowl combine blue cheese crumbles, buttermilk, sour cream and yogurt. Set aside.
Remove the sweet potatoes from the oven and place on a serving platter. Spoon the blue cheese mixture over the sweet potatoes followed by pickled walnut salsa. Serve and enjoy!