Gather your ingredients. In a large bowl, mix the hot water and demi glace together until blended.
Reducing the wine over medium heat. We are going to reduce this all the way down to 2 tbs (crazy right???). This is likely going to take at least 15 minutes if not longer.
This is what that small bottle of wine has turned into. So much packed flavor!
Add the wine, salt, Worcestershire, black pepper, and black mustard into the Demi Glace. Stir and then add the grated garlic. Stir further.
Add your butter and the thyme.
After you've gotten it fairly well mixed up, I'd suggest putting it into a mechanical mixer and run it on medium speed for a few minutes. Otherwise you'll be spending all day getting that liquid integrated into the butter.
Spread the butter out on parchment paper. Use a butter knife to smooth it and shape it. It should look like a 1" thick plate of fudge.
Make it your own now. Cut the butter into squares, circles, stamp your initials ;-)…. whatever you like. I used a shot glass to stamp out little circles. I find that to be the perfect size for a nice sized steak.
Cover the butter and transfer it to the fridge to firm up a bit before further handling.
Put the butter on the next steak you cook, or melt it over a starch.