Marshall Field’s in the WWI era

Thank for this WWI era recipe hosted by Recipezazz at https://www.recipezazz.com/recipe/marshall-fieldas-potato-flour-muffins-23404. The site explains, “During the First World War, cooks were strongly urged to reduce the use of wheat in their recipes. In Chicago, the Marshall Field department store began serving muffins made from potato flour in its restaurants. The wheatless muffins, rather than being seen as a hardship, became a much-loved staple still on the menu in the 1940s, maybe longer.”
8 servings

Ingredients
5 egg whites
2 1/2 t. granulated sugar
1/2 t. salt
2 1/2 T. ice water
3 egg yolks (slightly beaten)
1 c. potato flour
2 t. baking powder

Beat sugar and salt into egg whites until stiff but not dry. Gradually add ice water. Add egg yolks. Sift flour and baking powder and add to mixture. Mix thoroughly and place in greased muffin tins. Bake in 400° oven for 20 min.