Combine the wine and shallot in a small saucepan and simmer over medium heat until reduced to about 2 T. (it will have a thick, syrupy consistency).
Let the red wine syrup cool, then stir into the softened butter with the rosemary and a few cracks of black pepper. Once fully incorporated, spoon the butter onto a large piece of plastic wrap. Fold the wrap over the butter and twist the ends to create a log of red wine butter. Place in the fridge until ready to use.
Preheat a grill, stovetop grill pan, or cast iron skillet. Season the steaks with salt and pepper and cook until medium rare (about 10-12 minutes). Remove the steaks and slice a coin of the butter of the top of each.