1) Preheat the oven to 425F.
2) Line a large baking sheet with parchment paper. Place the cauliflower on the baking sheet, and brush the “steaks” and florets with olive oil. Sprinkle with salt and grate enough parmesan cheese over them until covered.
3) Roast until lightly caramelized and almost cooked through, about 30 minutes.
4) While the cauliflower is roasting, prepare the pesto sauce. Place the pistachios, olive oil, basil, parmesan (about 1/4 cup), garlic and salt on a small food processor and blend until smooth. Adjust salt and olive oil to taste.
5) Arrange the cauliflower steaks on a large plate and drizzle with the pesto, garnish with more pistachios and fresh basil if desired.