From Lauraine Jacobs in the Listener - makes 10 muffins.

3 juicy limes
60g butter, melted
2 large eggs
200g plain flour
2 1/2 tsp baking powder
100g sugar
1 cup peeled and diced feijoas

Preheat oven to 180C; line a 12 muffin tray with paper cup liners (don't decide not to, they go sticky!)
Use a zester to strip the zest of 1 lime, then juice it and the other two. reserve the zest aside for the top of the muffins.
Add the lime juice to a bowl with the butter and eggs, and whisk until light and fluffy (it's actually far too liquid with the melted butter, juice and eggs to whisk into anything, but it didn't matter).
Sieve the flour and baking powder together (I just ran them thru with a whisk) and fold into the butter mixture, with the sugar (given how liquid it is, you actually have to stir!).
Fold in the chopped feijoas. Spoon into 10 muffin holes, and sprinkle tops with extra sugar and the lime zest.
Bake 20-25 minutes until golden and firm to the touch.