Should you need cake flour where there is none, you could have added 1/2 cup corn starch to your ap flour, making up that missing 1/2 cup of flour.
Did you sift said ap flour before measuring? Sifted flour is lighter than unsifted.
I am a fan of making the recipe, weigh all ingredients, figure out the percentages so when you need to convert for more or less you can keep the correct ratios.
When tripling a formula, the liquids usually get off balance - sounds like you had too much liquid, and maybe needed to scrape the bowl and combine the batter better.
Little butter and sugar got left un-mixed |