Preheat oven to 375°F. Place a baking dish with some water in it on the lowest shelf of the oven to create steam.
Pull the outer leaves of the cauliflower off and cut off the stem. Using a paring knife, carefully cut out part of the core (about an inch of it) so that the cauliflower can sit flat. Be careful not to cut off the florets.
Place the cauliflower cut side down in a seasoned cast iron skillet. Drizzle the olive oil all over the cauliflower, rubbing it into all of the crevices. Sprinkle with salt.
Roast the cauliflower on the middle shelf of the oven until tender, about 60-75 minutes. Baste the surface with olive oil occasionally as it cooks.
While the cauliflower is cooking, make the pesto. Place the basil, almonds, cheese, garlic, vinegar, salt and pepper in a food processor and pulse until finely chopped. Stream in the olive oil and continue to process until it is almost smooth but still has a little texture. Transfer to a bowl. Stir in 1-2 tablespoons of water to thin the sauce out slightly.
To serve, spread some of the pesto out on a plate and carefully place the whole roasted cauliflower on top using a spatula. Sprinkle with golden raisins and Marcona almonds. Cut into wedges and serve.