Hi Grandma Sue;
Here is the recipe, it is in a cookbook of brand name recipes.

ALL-TIME FAVORITE PUFF PUDDING
Although this interesting pudding did not appear on the Post Grape-Nuts package until 1952, it was originally developed for a book about Post Cereals founder C.W. Post, way back in 1926. It's a lovely dessert with a cakelike top layer and a creamy, lemony custard below.

1/4 cup butter or margarine
1/2 cup sugar or honey
1 tsp. grated lemon rind
2 egg yolks
3 Tbsp. lemon juice
2 Tbsp. all purpose flour
1/4 cup Post grape-nuts cereal
1 cup milk
2 egg whites, stiffly beaten

Thoroughly cream butter with sugar and lemon rind. Add egg yolks; beat till light and fluffy. Blend in lemon juice, flour, cereal and milk ( mixture will look curdled but this will not affect finished product) Fold in beaten egg whites. Pour into greased 1 qt. baking dish. Place the dish in pan of hot water. Bake in 325* oven for 1 hour and 15 minutes, or until top springs back when lightly touched. When done, pudding has a cakelike layer on top with custard below. Serve warm or cold, with cream or whipped topping, if desired. Makes 4-6 servings

Note: For individual puddings, pour mixture into five 5oz. or four 6 oz. custard or souffle cups. Bake for about 40 minutes, also in pan of water.