This is gorgeous. It's not everyone's cup of tea -- chances are, if you don't like strong tastes like horseradish with your beef, you're not going to want blue cheese. But if you do, this is seriously good stuff.
For stock, use vegetable, beef, or instant stock made from a stock-cube such as Bisto, Oxo, Knorr, etc. Use a mild blue cheese. Use a heavy cream, the heaviest you have on hand. Instead of heavy cream, you can try the same amount of cream cheese, or Greek yoghurt, or the same amount of milk with a teaspoon of flour whisked into it. If you go the milk and flour route, let it cook first a bit in the stock before adding the blue cheese. Don't use regular yoghurt, however, it wouldn't survive the temperatures; it would curdle.