ID help - ?kale with a white edge?

Hello! I'd like some help IDing what I'm pretty sure I bought as a kind of kale perhaps last year.   I bought it here in Scotland as a smaller plant, not as seeds.  But, raw, it tastes unpalatably bitter unlike curly kale or the cavolo nero that's also in the garden.  The leaves are quite flat, quite a pale green with a waxy covering that's almost oily.  Cabbage worm does lay on them.  Many leaves have a distinctive white edge which I have not been able to identify online.  I started to wonder if I was mistaken about it being kale but have just roasted some leaves and cooked it does taste delicious just like kale crisps. Any ideas if it is kale and if so which type?