This recipe is from the post: Get Sauced.

From the cookbook Favorite Florence Foods and attributed to Jane Foxworthy Cubbage

1/2 stick butter (4 Tablespoons)
2 squares bitter (unsweetened) chocolate
1 small can (5 oz.) Evaporated milk (do not used condensed)
3/4 cup granulated sugar
1/2 teaspoon good quality vanilla extract (I use Madagascar Bourbon)

Melt butter and chocolate over low heat; add milk, then sugar. Bring to a boil, stirring often. Remove from fire, then add vanilla. This will keep for some time in the refrigerator…at least a week, but good luck not eating it before then!