Bring vinegars and sugar to a boil, and pour over sliced red onion. Submerge onion rings and let cool to pickle for 24 hours.
Heat oven to 425°. Toss cauliflower florets with olive oil, salt, and pepper flakes. Bake on a sheet pan for 15 minutes. Florets should be lightly browned and tender; if not, return to oven for a few additional minutes.
Heat a large skillet (enough to fit cauliflower) to medium-high heat, and add a light coating of olive oil and cauliflower. Season with a pinch of salt. Add butter and return to oven for 4 minutes until butter browns and becomes nutty in aroma.
Remove from oven and add raisins and parsley. Place cauliflower on serving dish and sprinkle breadcrumbs on top, drape with drained onion and sliced ricotta salata. Appetizer serves 2