How do I freeze the screen so I can use a recipe?

Settings>General>Auto Lock>Never. The iPad will not go to sleep this way. If you want to lock screen rotation - use the side switch or if that doesn't work - double tap the home button, swipe to the right in the task bar - and lock the screen in there. The lock icon will be all the way to the left.

You're quite welcome. Assuming that you wanted to keep the iPad from sleeping - Don't forget to adjust the sleep time when you are done - if you never let the iPad sleep, the battery will drain faster.