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 Ruby grapefruits are in the shops in abundance at the moment.  I usually have a few in the fridge, but I tend to overlook them in favour of simpler fruit like apples or grapes.
It’s strange really, I’ll happily spend hours in the kitchen kneading dough or stirring risotto, but the thought of spending 2 minutes slicing and segmenting a grapefruit just brings out the laziness in me – even though I know I’m going to enjoy the taste much more than nibbling my way around the bruised bit of my boring apple.

I was thinking about this the other day whilst also looking at a book on flavour combinations that I’d heard of a while back, and the thought struck me – grapefruit and brown sugar! Mmmmm
I considered making a grapefruit drizzle cake, but thought it would be fun to try something a little more adventurous.  So my ‘Ruby Grapefruit cake with brown sugar buttercream’ idea was born.  In an effort to reduce waste (definitely nothing to do with a desire to make some sweeties), I thought I’d give candied grapefruit peel a go too.

Ruby Grapefruit Cake

The results were really tasty, albeit rather sweet.  I went a bit over the top with the buttercream, so ended up serving the cake with some grapefruit chunks on the side in order to balance the sweetness.

I think this recipe would also be great as a cupcake with a nice dollop of grapefruit marmalade in the centre.

Ruby Grapefruit cake with brown sugar buttercream (serves 12):

Ruby Grapefruit cake:

  •  225g golden caster sugar
  • 225g unsalted butter, room temperature
  • 3 large eggs and 1 egg yolk
  • Juice and zest of half a ruby grapefruit
  • 50ml milk
  • 225g self-raising flour
  • 1 tsp baking powder

Brown sugar buttercream:

  •  375g unsalted butter, room temperature
  • 375g light brown soft sugar
  • 375g icing sugar
  • 75ml milk
  • 1tsp vanilla extract

Candied grapefruit peel:

  • Skin of 2 ruby grapefruits, thinly sliced (I used the special bit that pokes out of my zester as this gives sturdy strips of peel that won’t fall apart and minimal pith.  It’s fine to just cut some strips off and slice thinly though)
  • 250g granulated/caster sugar
  • Water


  • 2 ruby grapefruits, peeled and segmented


  1. Preheat the oven to 190c, line the bottom of a deep 9 inch diameter cake tin with baking parchment
  2. Make the candied peel first.  Put the strips of grapefruit peel in a pan, cover with water (so it’s about a centimetre above the peel) and bring to the boil.  Drain the peel and repeat another two times (this takes some of the bitterness out of the peel.
  3. Dissolve 200g of the sugar in a cup of water using the same pan, bring to the boil and let it bubble for a couple of minutes, then add the peel back in and let it bubble gently for about 30 mins.  Be careful to make sure it doesn’t boil dry.
  4. Drain and pat dry then roll in the remaining sugar.
  5. Next make the cake.  Cream the butter and golden caster sugar until pale in colour, then stir in the grapefruit juice, zest, eggs, egg yolk and milk.  Mix in the flour and baking powder until you can’t see any more traces of flour.
  6. Pour into the prepared tin and bake for about 40-45 mins.  Check it’s cooked by inserting a skewer into the centre of the cake.  If it comes out clean, the cake is cooked. Take out of the oven and leave to cool for a few minutes before removing from the tin and leaving to cool on a cooling rack.
  7. Make the buttercream by creaming the butter with the brown sugar for a couple of minutes.  Once incorporated, add the icing sugar, milk and vanilla extract and continue to mix for a few minutes.  The buttercream will go paler in colour once ready and you shouldn’t taste any graininess from the sugar.  The consistency should be firm, but still soft enough to spread without tearing the cake.  If it feels like the buttercream is too firm, just add a bit more milk.  You can set this aside now until the cake it cool enough – just give it a quick stir before using.
  8. Once the cake has completely cooled (needs to be cooled to ensure the buttercream doesn’t melt as soon as you put it on) then divide the cake into two layers.
  9. Place the bottom layer on a plate and spread on a thin layer of buttercream.  Top with two thirds of the grapefruit segments.  Spread another thin layer of buttercream on the inside of other cake half (like you’re buttering a sandwich).  If you’re worried you’re going to break the cake, then just dab little blobs of buttercream on the grapefruit pieces on the bottom layer instead.  You don’t need to be too precise, this just to protect the cake from going soggy due to the juice in the grapefruit.
  10. Place the top layer of cake on and the spread the rest of the buttercream on top of the cake first (using a palette knife dipped in hot water and then dried to help it spread) then splodge buttercream around the sides and spread evenly.
  11. Top the centre of the cake with the remaining grapefruit segments and sprinkle on some of the candied grapefruit peel.

This cake will keep for a few days wrapped in foil, but it’s a good idea to remove the fresh grapefruit off the top during storage to stop the grapefruit juice seeping into the buttercream.


(My youngest after waiting very impatiently for the first slice!)