I made these yesterday. Three problems:
1 - the blueberries sank
2 - it made 15 instead of 12 muffins
3 - there's only me to eat them
I've got through two so far and given 4 away. 10 left. I thought I might be meeting an ex-colleague this afternoon, who is visiting from the USA until Tuesday, but I didn't get a confirmation. That's one less potential scoffer of muffins. They won't keep all that long either.
