Leaf lettuce is sweet if picked while young and tender, but a person has to stay on top of it as it quickly gets old, tough and can be bitter right before it bolts.
I was pretty pleased with how I did seedlings last year and I'll be repeating that this year. The plants I started as seedlings were stronger and produced better than those bought at the nursery as plants, so I'm going to try to do more seedlings here this year so we won't have to fill in much with nursery stock.
I just used a seedling tray for some of them and a big porcelain restaurant tray for the others, mixed leaf mold, some of the composted litter from my coop, and some quality potting soil for my seedling mix and placed these trays in the window light with heating pads under them. Kept them turned so they would grow evenly.
This year I'll be doing the same except, once they are up tall enough, I'll be covering the soil with some composted leaf matter to retain the moisture.