Hi Audrey, I don't recommend doing one large pavlova as it will take a ridiculously long time to cook I can't tell you the the time and temperature because I've never done one for 20 but if I had to guess I'd say you'd want to lower the temperature at least 50 degrees and you'd be looking at a baking time of 3+ hours with another 3 hours or so with the oven door slightly propped open. But again I've never done this and it's a total guess.

Thank you.

Hi Jacquelyn, the most likely culprit is that they weren't in the oven long enough. Unfortunately it's difficult to give an exact amount of time they need to be in the oven for as most ovens are off by +/- 20 degrees. Also things like humidity can effect baking times as well. Pavlovas should have a crisp shell on the outside and they should be soft and marshmallowy in the center. So if they're not feeling crisp on the outside yet, leave them in the oven longer. You can also try and leave the door cracked open a bit, which should air with the air circulation.