I took this to a coffee and cards and told everyone it was a lime cake, not a courgette cake, it was very strongly lime flavoured. It makes a lovely moist sponge and with the lime was quite ‘refreshing’ according to one taster. 
There are reasons why I modified it but they all hinged around making this a dairy free cake. That meant I didn’t try and do a cream cheese icing on top (dairy free cream cheese is, in my opinion, just yuk, though with plenty lime it might have been ok I didn’t want to risk it). Then there was supposed to be a lime or lemon curd filling and as I didn’t have the time or energy to make my own I shop bought one, only to realise seconds before putting it on that it contained butter, if I had made my own I could have made it dairy-free.
So here is my version:
Ingredients
250g courgettes (2 large ones – zucchini if you’re across the pond)
2 large eggs
125ml vegetable oil
150g golden caster sugar
225g plain flour
3 1/2 tsp baking powder
1/2 tsp bicarbonate soda
2 x 20cm sandwich tins, greased and lined (I only lined the bottom but it is definitely easier if you line the whole tin!)
Filling
1 jar lemon and lime marmalade (in my case a last minute decision, and a home made marmalade found hiding at the back of the cupboard!)
Icing
300 g icing sugar, sieved
100g dairy free spread (I use ‘Pure)
juice of 1 lime
To decorate
2-3 tablespoons of chopped pistachio nuts
lime zest curls
Method
Preheat oven to 180 degrees C
Wipe the courgettes, don’t peel them and grate but not too finely as they can go a bit soggy. I squeezed out some of the excess juice before I added them but you can decide how squishy they are.
Put the eggs, oil and sugar together in a bowl and beat with a hand mixer until creamy. Sieve in the flour, baking powder and soda and beat again until well combined. Stir in the courgette, pour mixture into tins and bake for 30 minutes. They should be slightly golden and firm to the touch. Leave in tins for about 10 minutes then cool on a rack.
To make the icing, beat the icing sugar and dairy-free spread with a hand whisk and add the lime juice. Add more icing sugar if necessary to thicken it. (To be honest I guessed the quantities above, I just made it up when I did it!)
Spread the marmalade over the bottom layer. Stack the second layer on top and cover with the dairy-free ‘buttercream’ icing.
Sprinkle with lime zest curls and pistachios just before serving (best to allow the buttercream to set a little first).
When serving you can decide what to call the cake. I started calling it lime cakeinstead of courgette cake and I did own up to the courgette after they’d eaten it!…and as for the lemon curd, well my husband loves the stuff and was delighted to be told he’s got a whole jar that’s been opened and needs to be eaten!no
Update August 2018, I can now get an Oatly dairy free creme fraiche which I think could be used to make an alternative topping with lime juice and some icing sugar. Haven’t tried it yet but confident it would work.