In a heavy, well-seasoned 8-inch cast iron skillet, melt one tablespoon of the butter over medium-high heat until the butter is foaming.
Add the refrigerated risotto, break it up into small pieces and spread them evenly in the pan with a large spoon, pressing down so they fill the bottom of the pan in an even layer.
Cook until the underside is well browned and crisp, 5 to 6 minutes. Shake the pan frequently to prevent the rice from sticking and press on it occasionally to help the pancake brown evenly.
Remove the skillet from the heat. Shake the pan to make sure the pancake isn’t sticking at all.
Slightly oil a plate large enough to hold the rice cake. This will help slide the cake off the plate back into the skillet.
Add the remaining tablespoon butter to the pan and heat until foaming.
Carefully invert the risotto pancake onto the plate. If some of the cake separates that ok. Once back in the skillet you can press down on the cracks and blend the cake back into an even shape.
Carefully slide the pancake back into the pan uncooked side down and continue swirling the skillet to make sure the pancake is loosened from the pan. Cook until the second side is brown and crisp, about 5-6 minutes and serve.