I came across this recipe for baked macaroni with peanut butter sauce in a Fannie Farmer cookbook from 1921. The addition of peanut butter makes it a bit of a strange recipe, and I’m not sure where the idea came from. The dominant taste would likely be the peanut butter, since there’s not much else in it. While the recipe calls for macaroni, at that time “macaroni” was a catch-all for any type of pasta, which is why the cook is supposed to break the macaroni into pieces–Farmer is likely referring to what we would call spaghetti today. 

Baked Macaroni with Peanut Butter
1 cup macaroni, broken in 1-inch pieces
2 cups milk
3 1/2 tablespoons peanut butter
1 teaspoon salt
3/4 cup buttered bread crumbs

Cook macaroni in boiling salted water twenty minutes, or until soft, drain in strainer, and pour over one quart cold water to prevent pieces from adhering; then put in buttered baking dish. Heat milk in double boiler, and add gradually to peanut butter. Pour over macaroni, cover and bake in a slow oven forty minutes. Remove cover, sprinkle with crumbs, and bake until crumbs are brown.

Source: A New Book of Cookery, by Fannie Merritt Farmer, Boston: Little, Brown,And Company, 1921, page 43.