This post may be too late but....
You could also make a roux

Equal parts of flour and butter
You would only need about 2 tablespoons to thicken about 1 litre of liquid
Melt butter in a non stick pan
Add flour slowly
Cook for a couple of minutes
If you want to use this to thicken a dark stock cook until the mix starts to brown
Add mix to your sauce and it should start to thicken within a couple of minutes