Melt the chocolate over low heat and set aside to cool. Sift the flour, baking powder, baking soda, salt, and sugar together into a large mixer bowl. Add the brown sugar, 2/3 cup of sour milk, shortening, vanilla, and red food coloring to the dry mixture. Beat on medium speed for 2 minutes, scraping the sides of the bowl several times while beating. Add the cooled chocolate, 1/3 cup of sour milk and the eggs and continue to beat, at medium speed, for an additional 2 minutes, or until well blended. Scrape the sides of the bowl frequently. Pour into two 9 inch prepared round cake pans. (Prepare by greasing and flouring pans.) Bake in a preheated 375 degree oven for 30 to 35 minutes or until the cake tests done. Cool in the pan for 5 minutes and turn out on wire racks to finish cooling until cold. Frost.