By our calculations, you should look at sowing Blushed Butter Oaks Lettuce about 53 days before your last frost date.
Bred by Frank Morton, Gathering Together Farm. 1
Blushed Butter Cos is a combination butterhead/romaine lettuce, with 10 inch heads of ruffly leaves in variable combinations of red and green. Many will be green with red tips.
Blushed Buttercos
1 http://www.territorialseed.com/product/3128/84