This was a better attempt at baking without butter, but although the flavour was vey good, the texture still wasn't quite right - it was quite dense and flabby, rather than moist and crumbly. I think this may be because I used a Greek style yougurt, which, ironically, has higher fat levels than most full-fat natural yogurts.
this recipe from Smitten Kitchen, although I didn't use the lemon juice syrup drizzle, as CT doen't like flavours which are too sharp. I only had 150g blueberries, which was about 1 cupful, so I added a small Cox eating apple, peeled and chopped into pieces about the same size as the blueberries. The moisture from the apples may also have contributed to making the texture denser than I'd hoped it would be. I think my loaf tin has different dimensions to the one recommended in the recipe - shorter and deeper - as the cake took 75 minutes to cook properly.
Although I wasn't completely satisfied with the texture, I think this is a recipe worth repeating. Smitten Kitchen suggests several possible variations, and I'd be interested in trying a loaf without fresh fruit - possibly with chocolate chips or nuts, using a lower fat yogurt or perhaps buttermilk.