Cousin Jane's Cookies with Baked Frosting

I'm imagining this is some kind of a bar that is frosted and then baked. Typical of the older recipes, there are very few baking directions.

Cream 1/2 c. shortening, 1 c. sugar & 2 well beaten eggs

Add 1/2 tsp. vanilla, 1/2 tsp. salt, 1 1/2 c. flour, 1 tsp. baking powder

Spread 1/4 in. thick on greased cookie sheet

Frost with white of 1 egg, beaten stiff. 1 c. brown sugar folded in, 1/2 tsp. vanilla