Karen and I eat a lot of salad and she prefers Romaine lettuce. Recently she heard that you could grow new lettuce from the old heads (or stalks or whatever you call Romaine lettuce things). After cutting off the tops and eating them, she put the base of the stalk in a shallow bowl of water, where
literally overnight new leaves sprouted.
These things seem to grow nearly an inch each day, even in the kitchen without natural light. I’ve put some of them in a pot on a south facing window sill and, as you can see, they are
4-6 inches tall, only days after I put them in the pot. I just dusted the bottoms of the stalks with some rooting powder we happened to have (I don’t think it’s necessary) and gently pressed them into the soil. They didn’t have visible roots when I did this, but they continue to grow.
Presumably, you could grow these in pots or in the ground and just cut them off when
they’re big enough to suit you and leave it to grow some more.