Chocolate-Marshmallow-Walnut Fudge with Sea Salt

I rejiggered the recipe for Campfire Marshmallow Fudge from A Book of 150 Recipes ~ Prepared with Campfire...Marshmallows (1928), because I love the booklet almost as much as I love the combo of marshmallows and chocolate. To avoid using a fussy candy thermometer, I used sweetened condensed milk, which produces a fudge-like consistency in less time. Deeply toasted walnuts and a generous sprinkling of salt cut the sweetness of the marshies.