In a bowl, place the butter, Vegemite and thyme. Season with sea salt and cracked pepper, and mix to combine, until nice and smooth. Spoon the mixture onto a piece of glad wrap, roll tightly and fashion into a log. Twist both ends and refrigerate until needed.
Preheat a BBQ to medium-high. Brush both sides of the steak with a little olive oil or melted butter to prevent it from sticking to the BBQ.
BBQ the steaks until golden brown and slightly charred, 4 to 5 minutes. Turn the steaks over and continue to grill 3 to 5 minutes for medium-rare, 5 to 7 minutes for medium or 8 to 10 minutes for medium-well or until done to your liking.
10-seconds from removing, add a few slices of the slightly hardened butter to the top of each steak. Transfer the steaks to a plate and rest under foil for 5 minutes, letting the yummy butter melt into the steak.