HELP, HELP....our popovers are sticking in the muffin pan

I am a chef, and at one point my career, I was the chef at The Swift House Inn in Middlebury, VT...I have made thousands of popovers. The best method, I have found, it's to pre heat the pans, then put a decent amount of oil our melted butter in the bottom of each cup. The hot oil makes them really pop and they won't stick. Not the healthiest, but tasty!