To remedy this situation, I bunged the whole bowl in the microwave for just long enough to soften that butter, then got the beaters back into the mixture again. All this extra beating made the creamed mixture very light and fluffy. I was quite pleased with it.
Until I started folding in the sour cream and dry ingredients, that is! I scooped the sour cream straight into the cake mixture from the pottle, when really I should have stirred it up a little first. This would have helped the mixture to combine, instead of just floating around the mixture in big lumps.
I eventually got the dry ingredients and all the sour cream mixed in to my satisfaction. I was sure I'd overmixed it, but otherwise it looked pretty good. I poured the mixture into a greased and lined springform tin, and put it in the oven for 45 minutes.
I took my lemon sour cream cake to work this morning to feed the hungry workmates. This one disappeared much faster than most of the things I bring in, partly because Sue cut it into fairly generous slices, but mostly because it was really tasty - I'd worried it would be a bit dense and soggy, but actually it was moist and deliciously lemony. I'm not sure if the appearance of the cake was what it should have been, but certainly the flavour was spot on.
Make a note of this cake. It's definitely worth a go. Two recommendations: make sure your butter is nice and soft before you start, and give your sour cream a bit of a stir before you add it, so you're not plonking in lumps of the stuff.