I am making these muffins but would like to freeze half the mixture - will this be ok or will it affect how they cook/rise/taste when I cook my second batch (from the frozen mixture)?
(Recipe contains - self raising flour, bicarb soda, golden caster sugar, chocolate, dried cranberries, butter, eggs, yoghurt)
Once you've got your wet ingredients in there the timer is running. The chemical rising action only lasts a little while, and you want as much of that as possible to happen while the muffins are in the oven. If you wait past that window your muffins aren't going to rise very well, if at all, and I think you'd definitely run into that with freezing the mixture.
Even if freezing the batter would stop the chemical reaction (which I seriously doubt), you wouldn't be able to make use of that fact. Using a conventional freezer, the cooling process is going to be fairly gradual. Your batter is going to be at an active temperature for quite a while before eventually reaching the mythical non-reactive temperature--far longer than the chemical rising action lasts. And then as you thaw the batter you have another lengthy period where your chemical clock is ticking, long before you can get it in the oven.
Muffins are a quick bread, same as waffles, so the answer to Can you freeze waffle batter? applies equally well here.
You can freeze it, and it will keep the batter from spoiling, but it will not maintain the quality. It won't rise very well when you thaw it and try to bake it.
I would suggest that instead, you freeze the wet and dry ingredients separately; measure them out into the portion sizes that you intend to use, and when you want to make more muffins, combine them after thawing them.
(Or, as Joe suggests - just freeze the finished muffins themselves.)
