When Do Popovers Rise?

Whisk in the butter, and let the batter rest for 15 minutes. After 15 minutes, the little lumps will have risen to the top.

Why do my popovers not rise?

When baking don't open it again until they're done. If you open the oven door the temperature inside can drop too quickly and the popovers will not rise properly. Whip the batter up really airy right before you add it to the pan they'll rise extra high.

What causes popovers to rise?

The hotter your oven, the higher your popovers will rise. Which makes sense: the faster liquid in the batter turns into steam, the more chance your popover has to expand before its crust sets.