We make blackened fish with cream sauce frequently and run into a problem with left over sauce. Every time we reheat it, the butter seems to seperate from the rest of the sauce and it never tastses the same.
The sauce is started witha roux and has cream, wine and parmesean cheese in it.
Try whisking it very well prior to heating and then just gently heating to simmer, continuing to whisk--dont boil, of course.
I think if you watch it and stir well, you could do it in the microwave also. A roux based sauce shouldn't really be that difficult to re-heat. The milk part is the delicate portion.
It won't reheat well at all in a microwave, and honestly, that's the only time i've ever had trouble with a sauce separating on me. You can do it on the stove in a regular pan you have, just keep the heat low and give it a few stirs every now and again.