Rhubarb and custard blondies are the perfect pick-me-up for spring days. The tanginess of the jammy stewed rhubarb pairs perfectly with the sweetness of the vanilla custard and blondie mixture. The brown sugar in this recipe gives these a deliciously chewy edge and the batter is crammed with delicate white chocolate pieces to combat the tartness of the fruit.

How to make the best rhubarb and custard blondies:

  1. Use a 9×9 inch baking tin like this one. The baking time specified in this recipe is based on making these in a tin this size. If you’re using a rectangular 9×13 inch tin, double the quantities for this recipe for larger blondies and add another 5-7 minutes onto your baking tin. Using a smaller tin? Reduced the baking time by 3-4 minutes.
  2. Make sure you don’t over-bake. It may be deceiving since the rhubarb and custard cause these to look a little wet when they come out the oven. However, there really isn’t anything more disappointing that a blondie that’s too tough to eat or lacks chew and gooeyness. These blondies will continue to cook as they cool down so remember the texture will change. Here’s what I look out for to know that they’re ready:
  • The batter is golden brown and has risen well
  • The edges are starting to shrink away from the sides of your tin, or small cracks have appeared in the batter
  • The custard has started to form a golden brown skin and the rhubarb and beginning to “char” just a little
  1. Make sure these blondies are completely cool before slicing. They’ll look amazing, smell amazing and in all honesty, you’ll want to dive straight in as soon as they come out the oven. The cooling period however is crucial if you want that thick jammy fruit and firm base (rather than a sloppy mess!). Make sure they cool for at least 15 minutes in the tin, and at least another 10 on a cooling rack. If you can bear it, pop the tin in the fridge for at least 4 hours or overnight to give your blondies time to set properly.

Ingredients and alternatives

Wondering how to substitute ingredients you might not have? Here’s a little breakdown of what you can use instead:

  • Plain flour: white spelt flour, rye or even a dedicated cake and pastry flour would be a great alternative in these blondies.
  • Rhubarb: these wouldn’t really be rhubarb and custard blondies without the rhubarb. However, if you’re struggling to pick any up from your local supermarket or grocery store, here are my favourite swaps: red plums, raspberries or strawberries (keep 50g whole rather than stewing for dotting on the top before baking, and reduce the sugar to 50g), or pitted cherries would be great in this.
  • Butter: always use unsalted! Unfortunately you can’t get away with using salted for this recipe.
  • Sugars: while this recipe calls for light brown sugar, you could also make these blondies with light muscovado sugar or a mixture of 100g dark brown sugar and 200g caster sugar. They may just taste a tad more caramel-y with the latter.
  • Vanilla: I personally love a vanilla bean paste for intense flavour and depth, however regular vanilla extract or essence can be substituted instead.
  • Chocolate: don’t have any white chocolate? You can leave this out of the recipe completely, or use MilkyBar buttons for ease.
  • Eggs: only have medium eggs? You can substitute the large egg in this recipe for one medium egg.

Troubleshooting these rhubarb and custard blondies:

Does my rhubarb need to be completely smooth?

The short answer? No. While we stew the rhubarb for 10 minutes, you may still be left with a few good chunks of fruit – and that’s totally fine. Simply fold it into the batter as per the recipe instructions.

What kind of custard should I use?

A thick, indulgent custard is what you want for this recipe, as opposed to something that’s a little more runny. Here are my top three choices:

  1. Waitrose No.1 Madagascan Vanilla Custard
  2. Ambrosia Deluxe Custard West Country Cream
  3. Judes Madagascan Vanilla Custard

My blondies have come out the oven but look too wet!

The sticky rhubarb and vanilla custard will add an element of moisture to the batter, but once your blondies have been removed from the oven, they’ll continue to cook in the tin. This thickens up the stewed fruit and causes the custard to solidify a little.

Rhubarb and custard blondies

Rhubarb and custard blondies

A classic blondie filled with white chocolate chunks and swirled with jammy stewed rhubarb and creamy vanilla custard.
Prep Time 30 minutes
Cook Time 30 minutes
Total Time 1 hour
Course Dessert
Servings 12 slices


For the rhubarb

  • 200 g rhubarb chopped into 4cm pieces
  • 100 g caster sugar
  • 1 tsp vanilla bean paste I like Taylor & Colledge
  • Few drops red food colouring
  • 2 tbsp water

For the blondies

  • 190 g plain flour sifted
  • 20 g Bird's Eye custard powder
  • 1.5 tsp baking powder
  • 170 g unsalted butter
  • 300 g light brown sugar
  • Pinch fine sea salt
  • 1 tsp vanilla bean paste I like Taylor & Colledge
  • 1 large egg at room temperature
  • 100 g white chocolate roughly chopped into chunks
  • 100 g ready-made vanilla custard


To make the stewed rhubarb

  • Cut the rhubarb into 4cm pieces and place in a medium-sized saucepan.
  • Add the sugar and vanilla, along with 2tbsp water and place on a low-medium heat on the hob.
  • Leave to simmer, stirring every now and then, for 10 minutes.
  • Add a few drops of red food colouring if you want that signature pink colour and stir thoroughly. Set aside to cool.

To make the blondies

  • Preheat your oven to 160C / 320F and adjust a rack to the middle shelf.
  • Grease a 9×9 inch square tin with butter and line with baking parchment.
  • In a medium bowl, sift the flour, custard powder and baking powder then mix to combine.
  • In a medium saucepan, melt the butter and sugar over a low heat with a pinch of salt, then remove from the heat and leave to cool completely.
  • Once the mixture has cooled, transfer it into a large bowl and whisk in your egg.
  • Add the flour mixture, stirring until just combined then add the chopped chocolate mixing until everything is nicely incorporated.
  • Using a rubber spatula, swirl through the jammy stewed rhubarb and vanilla custard, leaving a little to dollop over the top.
  • Transfer the batter into the prepared tin and smooth into an even layer. If you're left with a little rhubarb mixture and custard, dollop onto the top of the blondie mix and use a knife to swirl.
  • Bake for 25-30 minutes until golden and bubbling.
    N.B. The rhubarb will have thickened slightly, and the custard will brown a little. While it may look a little wet in the centre, the blondies will continue to cook once removed from the oven.
  • Remove from the oven and leave to cool in the tin for at least 15 minutes.
  • Lift the blondies out of the tin and transfer to a wire rack to cool completely then slice and enjoy!
Keyword blondies, brownies, caramel, chocolate, custard, rhubarb, spring, traybake, vanilla, white chocolate

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