Most dairy products freeze well:
– milk up to 1 month
– yoghurt up to 2 months
– double or whipping cream up to 2 months
– butter up to 3 months
– grated cheese for up to 4 months
Double cream can go a bit grainy if frozen, so just whip it lightly before freezing. Single cream doesn’t freeze so well and can go watery.
To use frozen dairy, just thaw overnight in your fridge before you need it (though small portions of things like frozen cream or cheese could be added straight into a hot dish).
Buttermilk adds a lovely sourness or springiness to dishes (a little like yoghurt), but if you don’t have any in the fridge, make your own by squeezing half a lemon into some milk and leave to sit for 5-10 minutes so that it curdles.
If you’re adding cold yoghurt into a hot dish, mix a teaspoon of cornflour into the yoghurt before you add it to stop it splitting (splitting will either leaving a runny clear liquid around the edge of your dish when you serve it or there’ll be blotches of white that don’t fully combine).