Line a heavy saucepan or skillet with 2 of the lettuce leaves.
Add the uncooked peas, mint and dots of the butter.
Sprinkle with salt and sugar.
Spread remaining lettuce leaves on top.
Cover pan closely and set over medium heat.
When steam begins to escape, turn heat low and cook slowly for 10 minutes.
Uncover and discard mint and lettuce.
Shake pan and leave uncovered while keeping hot, so that peas will stay as green as possible.