Baby Spinach, Celery Root, and Fuji Apple Salad with Creamy Pistachio Dressing

This salad is another Aarti Sequeira masterpiece. She calls it The Ugly Duckling Salad because of the celery root component which is sort of the "ugly duckling" of the vegetable world. It's gnarly and unattractive on the outside, but inside lies a beautiful, creamy and healthy vegetable.
I've long been a fan of celery root, which is what first attracted me to this recipe. Celery root makes a great potato substitute because it has a much lower glycemic index, and it's much lower in carbs and calories - steam it and make mashed "potatoes", thinly slice it to make a "potato" gratin, and the list goes on. For some reason, I hadn't tried it raw, though. I discovered it's delicious raw - mild in flavor and it added an almost creamy texture to the salad.
Serves 4
Dressing:
1/2 cup shelled pistachios
2 large cloves garlic, roughly chopped
1 lemon, juiced
1/2 teaspoon Sriracha sauce
1/2 cup hot water
1/2 cup canola oil, plus more if necessary
Kosher salt
freshly cracked black pepper
splash of extra-virgin olive oil
In skillet over medium heat, toast pistachios until lightly browned.
In blender or food processor, place toasted pistachios, garlic, lemon juice, Sriracha sauce, water, and oil, then blend till smooth. Add salt and pepper to taste. If too watery, add more canola oil and blend to emulsify. Add drizzle of extra-virgin olive oil and blend once more. Set aside.
Salad:
1 bag baby spinach, pre-washed
1 Fuji apple, thinly sliced
1 celery root bulb (about the size of a softball or smaller), peeled and grated (see below)
In large bowl, place spinach and apple slices. To prepare celery root, wash thoroughly, then cut outer peel away from bulb revealing white inside.