Windowsill Sage - Compost going Mouldy

I have tried (am on my 2nd attempt) to grow Sage on my sunny window-sill, this time the plants are large & healthy and look great, but I have noticed the compost is/has gone mouldy.   

Do I leave them as they are?
Do I scrap the mould off?
Do I remove the plants from mouldy compost and replace? 

As you can guess I have no idea but really really really want to preserve the life of the herbs.   

My other half is a chef and wants to put them in some stuffing!!    Not an option just yet!! 

It needs to be outside. It will be much happier in garden soil with room to grow. Sage is hardy and will survive outdoors with no problems.

Oft sage is as tough as nails! We had one plant in a pot on the patio for years until it got stupidly big so when we moved to this house (with a little bit growing space in the ground) I bought another little plant which was relatively ignored and rarely watered, and it flourished! In the end I got rid because the bush got huge and we hardly ever use sage!

Common sage is 100% hardy here, although it does have the well drained soil it requires, and does look a bit bedraggled at the end of winter.

It can be pruned quite hard in spring, just make sure that you don't cut below the last little bud on the stems whether woody or not, and it will come back a treat. Some of the more specialist varieties may not be as tough or respond as well to hard pruning as the common types though.

As an insurance, it is one of the easiest to strike from stem cuttings - I keep a few growing in a corner of the garden as spares, although they usually end up going to other people. 

You have to take into account your heat zone for sage. I'm in zone 4/5 and sage will die if left out over winter, so definitely not a hardy perennial. We have to replant sage every year. Generally, the UK is milder than my winters but up north UK it can almost match my winters.