Yes, you can use this method for cooking a box of Uncle Ben's, but you want to determine how much rice/pasta is in the box and then decrease the liquid amounts accordingly. Keep in mind, there is little to no evaporation when pressure cooking, so you would not follow the instructions on the back of the box if pressure cooking. Although I don't have a box here to measure, I would estimate that 1 box is probably equivalent to ¼ of this recipe. So, for 1 box, your liquid amounts would be about ½ cup.