cauliflower

I've never had much luck growing cauliflowers!

So, I live in SW France, it's dry and hot in summer. I always buy little plants and pop them in either in early spring or aug/sept time. The result is generally the head shoots rather than staying compact. Cabbage grows exceptionally well (loads of cow muck + a little agricultural lime)...and romenesco, but never cauliflower 

This year, I thought I'd cracked it. Planted in spring, had lots of rain through April, lovely little head forming by May. They've suddenly got enormous, so all good. But they've now started to get purple edging to the florets. What's going on? Any suggestions very welcome 

ahh, rubbish. I thought as much....

Is it best to freeze blanched florets, or just make a puree and freeze that?

Any tips for beautiful cauliflowers?