To sear, I used my cast iron skillet. I set my burner to medium/high heat and waited 6 minutes for it to heat up. During this "rest time" the steak went from 110F to 112.5F. I then added my grapeseed oil to the pan and waited for it to shimmer in the pan.
High Smoke Point Oil
I then took my porterhouse on edge to render some of the fat on the NY strip side for 10-20 seconds.
I then laid the porterhouse flat on the cast iron skillet to sear. You want to sear for around 30 seconds and then flip the steak over to a new section of the pan. Repeat this for a total sear time of 1 minute on each side. Then take the pan off the heat and take the porterhouse out of the pan. The goal here is to allow the pan to cool - do this for around 2 minutes.
Then add unsalted butter to the pan and allow it to froth.
2 tbsp Unsalted Butter
Once the butter is frothing, add the porterhouse back to the pan at the top of the skillet. You then want to angle the skillet so that the porterhouse is in the air on the pan on one side and the frothing butter on the other. Then with your spoon, baste each side of the porterhouse for 30 seconds then flip and baste for another 30 seconds; Repeat this process for a total of 1 minute on each side. After searing and basting, take the steak out of the pan.