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Vegan rhubarb crumble cake with custard buttercream

4.67 from 3 votes
Total time: 2 hours 10 minutes
Vegan rhubarb crumble cake on a plate on top of a wooden table

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So have you heard of the magical creation that is the ‘crumble cake’? Well, until a few years back, neither had I. But upon hearing about it, there was no question that I had to create my own.

It turned out that taking a trusty sponge recipe and fusing it with the elements of a crumble works.

And, wow, does it fit perfectly with the change in season. A light fluffy sponge, a crispy crumble topping, little bite-size pieces of fresh, fragrant rhubarb smothered in the creaminess of the icing. Come on, what more could you want?!

The real beauty of the crumble cake is that it’s served cold. So you get all of the flavour of a crumble, but none of the warm stodginess that you prefer to keep to the colder months.

Servings: 8 Slices



  • 5 tbsp Linseed or flaxseed
  • 266 g Water or 15 tbsp
  • 200 g Golden caster sugar
  • 250 g Vegan butter
  • 300 g Plain flour plus 80g for the crumble top
  • 2 tsp Baking powder
  • 1 tsp Ground cinnamon
  • 1/4 tsp Ground nutmeg
  • 300 g Rhubarb finely sliced


  • 200 g Icing sugar
  • 100 g Vegan butter
  • 3 tbsp Vegan custard powder many supermarkets own brand are accidentally vegan, plus a few of the big brands


  • Preheat your oven to 180 degrees (160 fan)
  • Grease and line 2 20cm round cake tins
  • Start by mixing the water with the linseed and then blend using either a stick blender or a stand alone blender until it turns globby and the seeds are broken down
  • Cream together the sugar and the margarine
  • Beat in the linseed mix until fully incorporated
  • Sift in the 300g flour and baking powder and then fold into the mix
  • Place 90g of the mix into a separate bowl and add in the 80g of plain flour along with the cinnamon and nutmeg
  • Using the back of a knife mix it together into a crumble type texture
  • Fold the rhubarb into the rest of the cake mix and then place evenly into the two cake tins
  • Scatter the crumble mix over the top of one of the cake mixes and then sprinkle over the 1sp of sugar
  • Place the cake tins in the oven for 40 minutes (check if this inside is cooked using a skewer)
  • Take the cakes out of the oven and allow them to cool completely
  • Whilst waiting for the cakes to cool, start making the custard buttercream
  • Place all the icing ingredients in a bowl and beat together until smooth
  • Spread the icing on top of the cake half without the crumble and then carefully place the crumble cake half on top to make a sandwich
  • And eat!


You can sub the rhubarb in this vegan crumble cake for all kinds of different fruits. Either experiment, or try out one of your favourite crumble fruits, like apple, cherry, or pear.

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Lucy Johnson

One response to “Vegan rhubarb crumble cake with custard buttercream”

  1. Penny avatar

    4 stars
    I wasn’t sure about this, but I had loads of rhubarb this year and there’s only so much stewed rhubarb you can eat. Glad I did! Made a nice change.

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