To make butter, place the red wine, shallot, peppercorns and bay leaf in a small pot. Bring to a simmer and reduced to a syrupy 2 Tbsp. Remove mixture from the heat and cool to room temperature. Remove and discard bay leaf.
In a mixing bowl, beat butter with an electric mixer until lightened. Add the wine mixture, mustard and tarragon or chives and beat until well combined, scraping the bowl with a spatula during the process as needed. Place a foot long sheet of plastic wrap on a work surface. Place the butter in an 8" long row down the centre of the plastic wrap. Roll the butter inside the plastic wrap, into a 2" thick log, gently twisting the ends to seal. Refrigerate butter until firm, at least 1 hour.
When ready to serve, set butter out at room temperature. Preheat an indoor or outdoor grill to medium-high. Season the steaks with salt and pepper. Lightly oil the bars of the grill, if prone to sticking. Grill steaks to the desired doneness, allowing approximately 2 to 3 minutes per side for rare, and 3 to 4 minutes per side for medium-rare. Unwrap butter and sliced into 12 rounds. Set a steak on each of 6 heated plates. Top each steak with two rounds of butter and serve.
Recipe Options: Serve the butter on any other tender steak, such as rib eye, strip loin or sirloin. Instead of green peppercorns, use 1 tsp. of coarsely cracked black peppercorns in the butter. Instead of tarragon or chives, use the stronger tasting chopped fresh rosemary or thyme, to taste, in the butter.