Recipe can be doubled and tripled with no issues.
Baking spray didn’t work as well as butter or margarine for greasing the cups. The point of popovers is to put as much air into the batter as possible so they will rise, so don’t skimp on the beating of the eggs and milk. Also the popovers cooked more quickly in my oven… at 10 minutes less. Since everyone’s ovens are different, just be aware that there is flexibility here. Good luck!