I can't remember if I commented on this before - last year I grew Tiara hybrid cabbage which William Dam seeds describes as a lettuce-like cabbage. It's early (45 day), not very big if spaced a little closer together, and very tasty.

I would certainly call it cabbage rather than lettuce - it's an excellent cole slaw cabbage, really tender and not very strong tasting.

I started some seeds the end of April and the heads have been ready to pick since early July. At this time of year when the lettuce starts going bitter and the spinach bolts, it's nice to have another option for something from the garden for salad.