Cottage Pudding with Vanilla Sauce

Cottage pudding is not pudding at all, but a simple yellow cake, baked in a square pan, and served with sauce, be it vanilla, chocolate, butterscotch, lemon, nutmeg, or even rhubarb. I consider it the perfect snack cake. I started with the recipe from Davis Cook Book: The Pure Food Kind (no date) and added an egg yolk, and a tad more butter and sugar, and I substituted buttermilk for the milk to make it more moist, flavorful, and tender. For the sauce