Preheat the oven to 425 degrees F. Cut off the cauliflower stems, then place the heads cut-side down and slice into 1/2-inch-thick steaks. Arrange on a baking sheet in a single layer. Drizzle with olive oil and sprinkle with salt and pepper on both sides. Transfer to the oven and bake until golden brown, 20 to 25 minutes, flipping after the first 10 minutes.
Meanwhile, add the pine nuts to a dry medium saute pan and toast over medium heat until golden brown, about 3 minutes. Add the raisins and butter and season with salt. Cook, tossing, until the butter has melted and coats the pine nuts and raisins. Off the heat, stir in the parsley.
Transfer the roasted cauliflower to a serving platter. Pour the pine nut-raisin mixture over the top. Season with salt.