Rhubarb Crumble Cake!

Easy, delicious, rhubarb crumble in cake form… what could be better than rhubarb crumble cake?!

So quite a while ago I shared my recipe for my apple crumble cake, and its always been a hit since. Apple crumble is probably the most common crumble, with rhubarb coming a close second… this could be completely wrong, but in my life its this way round.

But anyway, since the day of posting my apple crumble cake I have had requests for a rhubarb version… so here it is! It’s ever so slightly different as this beauty is in traybake form, but it’s still a gloriously delicious crumble in cake form. 

Traybake Cakes

I didn’t want to make the cake the exact same as my other one, so it’s just a traybake cake version. You could say this is boring, but I bloody love a traybake cake. It’s much easier to chuck cakes into a tray, and go; no layering or anything.

My other traybake cakes such as my chocolate fudge traybake, and my gin and tonic traybake are larger in size, but that’s okay. I just wanted to make a smaller one for this beauty to use the correct amount of rhubarb. 

Rhubarb 

I often find that regular rhubarb is a lot greener, and can taste more tart in comparison to forced rhubarb, but I do think its a matter of preference… and what you can find in the shop.  Often forced rhubarb ends up a tad softer than the regular.

You can see the chunks of rhubarb in every slice, and it’s just beautiful. I’ve used regular rhubarb, and forced rhubarb, and both have worked well. I don’t cook my rhubarb before baking, as I often find it softens enough after being in the oven for over 30+ minutes!

So you have two options here. My way, and the easiest, is to use the rhubarb raw and chopped, it softens beautifully in the oven and you get lovely juicy chunks in every slice. I have tested this with both regular and forced rhubarb without pre-cooking either, and both work a treat in this traybake. If you would rather a softer, jammier result with no chunks, you can gently cook the rhubarb down first, and I have popped that optional method just below.

Preparing the rhubarb (optional step)

This step is completely optional, only do it if you want a softer, more jammy rhubarb running through the cake rather than distinct chunks. Pop your chopped rhubarb in a pan with a spoonful of sugar and a splash of water, and cook gently for 5 to 8 minutes until it just starts to break down.

Let it cool, and drain off any excess liquid before folding it into the batter, otherwise the extra moisture can make the sponge dense. Use this if your rhubarb is very thick and stringy, or if you simply prefer that softer texture. For everyday ease though, raw chopped rhubarb is honestly all you need.

Cake

The cake is basically just a regular sponge cake, with rhubarb added in, and crumble mixture on top. It therefore takes a little longer to bake, but thats totally okay. The added moisture from the rhubarb keeps the cake soft as well and prevents it getting dry. The crumble part is completely optional, but its just so damn good.

The cake itself is made up of butter, sugar, flour, eggs and these are beaten together to a normal cake mixture. I flavour it with some ground ginger, some vanilla extract, and then of course there is rhubarb throughout the cake as well. 

Because of all that lovely rhubarb moisture, this bakes a little longer than a plain sponge, around 40 to 45 minutes. You know it is done when the crumble top is golden and a skewer pushed into the centre of the sponge (not into a rhubarb chunk) comes out clean. The crumb should be soft and moist, never dry, thanks to the rhubarb baked all the way through.

Crumble

You can use a shop bought crumble mixture if you want, there is no shame in this. However, I have made my own using some caster sugar, unsalted butter and plain flour. It’s really easy to make yourself, so you should if you could. 

I always add the crumble ingredients into a bowl, and then rub it together with my fingertips to a crumbly breadcrumb texture. You want to use your fingertips with colder hands so that the butter doesn’t start to melt. To make it easier, you can grate the cold butter into the bowl first so it takes less time. 

If your crumble isn’t coming together quite right, it is easy to fix:

• Too wet or sticky and clumping into a paste? Add a little more plain flour and rub through until it turns back into loose crumbs.
• Too dry and powdery, not clumping at all? Add a little more cold butter and rub in until you get those lovely breadcrumb clusters.

Adaptions

This traybake is the main version and the one I would always reach for, it is the easiest and works every time. If you fancy it, you can also turn it into a layer cake like my apple crumble cake, using the same quantities and method and simply swapping in rhubarb. Just know that a layer cake can turn out slightly mushier than the traybake because of the rhubarb moisture, though I have done it a couple of times and it was fine.

The best topping if you made this into a layer cake however, would be to make it CUSTARD FLAVOURED! Imagine it… Rhubarb Custard Cake! Heaven basically. For a two layer cake, I would use… 250g unsalted butter, room temperature, 500g icing sugar, 1/2tsp vanilla extract, and 75g custard powder! Its basically the same recipe as I use in my custard cream cupcakes, and its a winner!

Tips & Tricks

• This cake will last for 3+ days at room temperature
• You can freeze the cake for 3+ months
• I use this 9″ baking tin in my recipe
• You can use shop bought crumble mixture if you prefer, or even leave it off if you don’t fancy it. 
• See notes above on making this a layer cake 
• The recipe has been updated in April 2024 – the only addition is ground ginger which is optional. 
• Line your 9″ tin with parchment and leave a little overhang up the sides, it makes lifting the whole cake out to cool so much easier and stops the edges sticking.
• If your tin isn’t brilliantly non-stick, give it a light butter under the parchment for extra insurance.
• Let the cake cool in the tin for a while before lifting it out by the parchment, as it is quite tender while warm.