Whenever I make a risotto, I always find that I need about 50% more liquid and 50% more cooking time than my recipe suggests. I recently made a Jamie Oliver risotto that called for 1 cup arborio, 2 cups chicken stock, and 20 minutes. I used more like 3 1/2 cups of stock and it took a good 30 minutes. My stock is heated in a separate sauce pan, and I add it a little at a time (although probably more than a ladle, maybe two?). I stir frequently but not constantly (probably once a minute). I consistently seem to have this issue regardless of the recipe source.
Am I do something wrong? Or is this a case of a recipe playing it on the safe side?