My grandparents used to lightly boil the small leaves on the top of their Brussel sprouts as a vegetable

The tops of the brussels sprout plant can be cooked and eaten as leaves.

Yes, as said, you can eat the leaves of the sprout plant, at one time you could buy sprout tops from the greengrocer, I sold some in that way when I was a teenager and my mother used the leaves in her soups.

It is a type of cabbage after all.

thanks for that, much appreciated