Finely grate the zest and juice the limes. Half, pit, peel and mash the very ripe avocados. Pit, peel and mash the very ripe avocados. Juice the limes. Sift the icing sugar.
- 1 Preheat the oven to 180°C/fan oven160°C/gas 4.
- 2 Grease and line the base of a 900g (2lb) loaf tin with greaseproof paper.
- 3 Using an electric whisk beat together the butter and sugar until light and creamy.
- 4 Add the lime zest and juice to the mashed avocado, then beat this into the butter mixture.
- 5 Add the eggs one at a time, beating well between each addition.
- 6 Stir in the vanilla extract.
- 7 In a separate bowl, sift together the flour, salt, baking powder and baking soda.
- 8 Use a large metal spoon to fold half into the avocado mixture.
- 9 Stir in the buttermilk, then fold in the remaining flour mixture.
- 10 Transfer the cake mixture to the prepared tin and smooth over the top.
- 11 Bake for 55 minutes - 1hr until a skewer inserted in the middle comes out clean.
- 12 If the loaf is browning too quickly, cover lightly with a piece of foil.
- 13 Remove from the oven then leave to cool for 15 minutes.
- 14 Remove from the tin, peel away the paper and leave on a wire rack to cool completely before icing.
- 15 To make the icing, mix the avocado with half the lime zest and the juice.
- 16 Cream the butter using an electric whisk, then beat in the avocado mixture.
- 17 Slowly add the icing sugar, whisking well to combine.
- 18 Spread thickly over the top of the cooled cake and sprinkle with the remaining lime zest.