This is my mother-in-law's recipe. She's been making it her whole life and whenever there is a potluck or family gathering, this is what she makes to bring. I don't remember ever eating lima beans before I met my husband and tried this dish but it surely was good. And when we served it baptism weekend my Mom didn't want to try it because she's "not a bean person" (her words). I told her to just take a taste (when did I become the parent?) so she did and then said she really liked them. So there! (Muah ... love ya Mom!)
The recipe below is as dictated by my mother-in-law as she was preparing it. There are not many measurements so the recipe will be more in paragraph form than anything.
Butter the sides of the pan and also add about 3 Tbsp butter to the boiling water. Then add 2 bags of lima beans (but these have to be fordhook lima beans, not baby lima beans ... to my mother-in-law this was VERY important). Add water to cover the lima beans (about halfway up the pan, cover and bring to a boil. Salt and pepper to taste.
When beans are cooked through, add half-and-half to bring to top of beans. Do not boil, but keep it hot. Dissolve about 3 Tbsp cornstarch with 1/2 to 3/4 cup of the heated half and half. Then add that back to the bean mixture and stir until thickened. Watch it because you may end up needing to use more cornstarch to get it to the proper thickness. Check seasoning and salt and pepper to taste.
Source: my mother-in-law