Can you use butter in a cast iron skillet?
Yes, you can use butter in a cast iron skillet. Cooking with butter in cast iron is great because it’s particularly non-stick and fragrant on a well-seasoned pan.
Some people have difficulty using butter because it tends to brown and smoke. This is typically because the pan is too hot. If you cook with lower heat, the butter will foam up and create a delicious cooking fat.
While cooking with butter in cast iron is great, butter should not be used to season new or restored cast iron cookware. Vegetable-based saturated fats (e.g. vegetable oil and shortening) will create a stronger, more non-stick seasoning.

Related Questions
Better not forget that butter
Using butter in your cast iron skillet can lead to delicious results, but if you use too high of heat or leave it on for too long, the butter and the rest of your food could get burnt onto the pan. When food is stuck on, clean your cast iron skillet carefully to avoid stripping the seasoning.