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OK, roast meat, remove meat, dispose of any excess fat. De glaze roasting pan with wine (red - beef, white - chicken etc).
Stir in good heaped tblsp plain flour. Gradually add veg water/stock made with a Knorr stock pot. (Vegetable only, others too salty)
I usually make a couple of pints.
Use what we need, then put rest in tubs, leave to cool, lids on, then freeze.
It's WHY it goes thin in the freezer is baffling me, straight out of the pan it's fabulous.