Trim the cauliflower head and cut into florets about 4 cm across. Rinse and drain well in a colander.
Heat the olive oil in a 30 cm / 12-inch deep skillet over medium heat. Add the garlic and chili flakes, cooking for 1 minute until fragrant, don't let the garlic brown.
Add the chopped anchovy fillets and stir until they dissolve into the oil, about 1 minute.
Add the cauliflower florets and toss to coat in the oil, cooking for 2 minutes.
Pour in the white wine and let it bubble uncovered for 1 to 2 minutes to cook off the sharp alcohol smell.
Stir in the crushed tomatoes, olives, and capers. Add a splash of water or broth if needed so the liquid comes about halfway up the florets. Season with salt and pepper.
Cover and simmer for 20 to 25 minutes, stirring occasionally, until a fork slides into the cauliflower with slight resistance and the florets still hold their shape. Add more liquid if the pan runs dry.
Uncover for the last 5 minutes if the sauce looks thin, letting it reduce and cling to the florets.
Taste and adjust the salt. Stir in the chopped parsley just before serving.