Sweet Cajun Blackened Steak can be on the table in 30 minutes, even if you don’t know how to blacken steak. The molasses in the sauce will do most of the blackening for you, so you don’t have to worry about undercooking the inside of the meat… unless, of course, you like it rare. —Christy Boston's Kitchen
Add the molasses, black pepper, red wine vinegar, salt, white pepper, savory, and cajun seasoning to a large bowl and whisk until well combined.
Pierce the sirloin several times on both sides with a sharp fork. This will tenderize the meat as well as allow the flavors to penetrate. Drop the steak into the bowl with the molasses-cajun sauce and toss to coat. Use your fingers to mush the steak into the sauce, then massage the sauce into the steak to really push in the flavors.
Heat the olive oil in a large cast iron skillet over medium-high until just smoking. Add the steak and sear it on the first side for 3 minutes, then flip and sear another 3 minutes. This will give you a medium temperature steak. Reduce the time a minute each side for more rare, increase it for more well done meat. The outside of the steak will become a bit charred and things will get a little smoky, but that's ok! You are blackening your steak... open your windows if you have to.
When done, use tongs to transfer the steak to a cutting board and place a pat or two of butter on top. Allow it to rest there for 10 minutes for maximum juiciness. When ready to serve, slice the steak against the grain into strips and plate it with blue cheese mashed potatoes, or put your steak on top of a salad (great for summertime!). Drizzle with any melted butter and accumulated steak juices that got left behind on the cutting board.