Hummingbird Bakery Mojito Cupcakes

It's National Baking Week this week so on Sunday I decided to make some Mojito Cupcakes from the Hummingbird Bakery's (@hummingbbakery's) Cake Days book.  I've had mixed success with recipes from their original book - the vanilla cupcakes and raspberry chocolate brownie bar are to die for; other recipes such as the cheese and spinach muffins just didn't work for me.

Nevertheless, I intend to have a go at more recipes from Cake Days as so far, everything I've made from it has been more than passable.  I picked these in particular because mojitos are my cocktail of choice.  Not that I drink many as according to my mother, one sniff of a barmaid's apron and I'm anybodys...

Mojito cupcakes - replete with mint leaves

So why am I posting on Tuesday about something I baked Sunday?  Surely that's cheating??  Well I baked the cakes on Sunday, popped to the shops, came home, started stocking the fridge and my little assistant took it upon herself to tip a newly opened box of icing sugar all over my kitchen floor.  At the time, I was less than amused.

No icing sugar, no frosting.  I finished them off tonight (decorating them, not eating them!) hence why I'm using this as a sneaky Tuesday recipe.

These are mini cupcakes and now they're frosted, I totally understand why.  They are VERY sweet and I can feel my teeth rotting just looking at them.  The sponge on its own is beautifully fragrant with a hint of lime and mint and a crunchy sugar-rum topping.  But the frosting just doesn't work for me.  It is too sweet and I feel it should be sharper.  Even adding lime juice didn't seem to cut through the sweetness.  I'd welcome suggestions on how to make really sharp lemon or lime frosting as it's something I've never found a successful recipe for.  Answers on a tweet to @lilmssquirrel.

Makes 12 medium sized cupcakes or 20-30 mini cakes

For the sponge:

100ml White rum 
170g Caster sugar
40g Unsalted butter, softened
120g Plain flour
1/4 tsp Salt
1 1/2 tsp Baking powder
1 tsp Grated lime zest
1 tsp Grated lemon zest
1 tbsp Finely chopped mint
1 large egg
120ml Milk 
1/2 tsp Vanilla essence 

Preheat oven to 170deg C and line a muffin tin with cases 

In a saucepan bring the white rum and 30g of the sugar to the boil, reduce by half and set aside. 
Beat together the butter, flour, salt, baking powder, lime and lemon zest, mint and remaining sugar. Mix until you have a crumb like consistency. 
Mix together the egg milk and vanilla in a jug and gradually pour this into the dry mix mixing until you have a smooth batter. 

Spoon cake batter into the cases up to 2/3 full. Place in the oven and bake for 12-15 min's for mini cupcakes or 15 to 20 for bigger or until the cakes are a light golden brown and springy to the touch. 

While the cakes are still warm spoon the rum reduction over them (1/2 tsp for mini cakes 1tsp for bigger approx) Then leave to cool completely! 

While the cakes are cooling, make and drink a mojito! ... erm I mean make the frosting! 

For the frosting

80g Unsalted butter
250g Icing sugar
1/4 tsp lemon zest
1/4 tsp lime zest
4 tsp milk
4 tsp White rum

1tbsp caster sugar
1 tsp chopped mint or lime zest 

Using and electric whisk, beat together the butter, icing sugar, lemon and lime zest until combined in a sandy consistency. Stir together the milk and rum and pour this into the butter mixture while still beating, whisk until light and fluffy. 
Divide the frosting between the cakes. To finish, mix together the caster sugar with either 1 tsp of mint or lime zest and sprinkle over the top.