Rhubarb and Custard Blondies

This tangy-sweet rhubarb and custard blondie recipe transforms the classic British flavor combination into a decadent traybake that perfectly balances creamy vanilla notes with bright, jammy rhubarb swirls. The custard powder in the batter creates an incredibly soft, melt-in-your-mouth texture that makes these blondies utterly irresistible.

I first made these blondies for a spring garden party and they disappeared within minutes. The vibrant pink swirls from the rhubarb always draw compliments, and guests are always surprised by how the familiar rhubarb and custard flavors work so beautifully in a blondie format.

Ingredients

• Butter: creates a moist tender crumb and adds richness to the blondie base
• Light brown soft sugar: provides depth of caramel flavor that complements the white chocolate
• Caster sugar: dissolves easily ensuring a smooth batter with the perfect sweetness
• Plain flour: gives structure while keeping the texture light
• Custard powder: is the secret ingredient that adds authentic custard flavor throughout
• Baking powder: provides just enough lift without making them cakey
• Eggs: bind everything together while adding richness
• White chocolate chips: melt into pockets of sweetness that balance the tart rhubarb
• Vanilla extract: enhances the custard flavor profile
• Rhubarb: should be bright pink for best color and flavor in your finished blondies
• Ready made custard: creates beautiful swirls on top use the thickest you can find

Step-by-Step Instructions

Prepare the Rhubarb Topping:

Place chopped rhubarb in a wide pan with caster sugar and water. Cook over medium heat for about 10 minutes until the rhubarb breaks down into a jammy consistency. Stir frequently to prevent sticking. The mixture should be thick enough to hold its shape when swirled but not watery. Set aside to cool completely before using.

Create the Base Mixture:

Melt butter with both sugars in a medium saucepan over low heat. Stir continuously until completely smooth and glossy. This slow melting process helps the sugars dissolve properly. Remove from heat and allow to cool for at least 10 minutes so it won't cook the eggs when added.

Prepare Your Workspace:

While the butter mixture cools, sift together flour, custard powder, and baking powder in a large bowl. This removes any lumps and ensures even distribution of the raising agent. Butter your baking tin thoroughly and line with parchment paper, leaving overhang for easy removal later.

Combine Wet and Dry Ingredients:

Beat eggs into the cooled butter mixture one at a time until fully incorporated. The mixture should look glossy and smooth. Gently fold in the dry ingredients using a spatula with a cutting motion to preserve air. Stop mixing as soon as no dry patches remain to avoid overdeveloping the gluten.

Add the Extras:

Stir in 150g of white chocolate chips and vanilla extract just until distributed evenly. The batter will be quite thick at this stage. Pour it into your prepared tin, spreading to the corners with a spatula for an even layer.

Create the Marbled Top:

Drop spoonfuls of cooled rhubarb mixture across the top of the batter. Add dollops of custard between the rhubarb. Use a skewer or toothpick to create beautiful swirls by dragging it through both toppings. Avoid overmixing the swirls they should remain distinct.

Bake to Perfection:

Bake in the preheated oven for 40-50 minutes. The blondies are done when the edges start pulling away from the tin and the center is set but still slightly soft. If the top browns too quickly, loosely cover with foil to prevent burning. Leave to cool completely in the tin.

Finish with White Chocolate:

Once cooled and chilled, melt the remaining white chocolate in short bursts in the microwave, stirring between each burst. Drizzle artistically over the top of the blondies for a professional looking finish. Allow to set before cutting into squares.

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My family recipe collection features many rhubarb desserts, but this one became an instant classic. The first time I served these, my daughter declared them "even better than rhubarb crumble" which in our house is the highest praise possible. The custard powder is my secret weapon here it adds that nostalgic flavor that takes everyone back to childhood puddings.

Storage and Make Ahead Tips

These blondies actually improve with a day of rest in the refrigerator, as the flavors meld and the texture becomes even more fudgy. Store them in an airtight container in the refrigerator for up to 5 days. You can also freeze them for up to 3 months wrapped individually in plastic wrap and placed in a freezer bag. Thaw overnight in the refrigerator before serving.

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Seasonal Variations

When rhubarb isn’t in season, this recipe works beautifully with other tart fruits. Try blackberries in late summer, cooking them down with a little less sugar as they’re naturally sweeter than rhubarb. Sour cherries make an excellent substitute in early summer, while cranberries work perfectly during winter months. The key is balancing the sweet blondie base with something tart for contrast.

Serving Suggestions

While delicious on their own, these blondies reach new heights when served slightly warm with a scoop of vanilla ice cream. For an extra special dessert, warm a square in the microwave for 15 seconds, then pour over additional warm custard for the ultimate comfort pudding. They also pair beautifully with afternoon tea or coffee as the creamy notes complement the bitterness of the beverages.

Frequently Asked Questions

→ Can I use frozen rhubarb instead of fresh?

Yes, frozen rhubarb works well. Thaw it first and drain any excess liquid before cooking it with sugar to create the jammy topping. You may need to cook it slightly longer to achieve the right consistency.

→ Why do the blondies need to chill for at least 2 hours?

Chilling allows the blondies to set properly, making them easier to cut. It also enhances their fudgy texture and helps the flavors develop fully. For best results, refrigerate overnight.

→ Can I substitute the custard powder?

If custard powder isn't available, you can use vanilla pudding mix as a substitute. The flavor profile will be slightly different but still delicious. Alternatively, increase the flour by 50g and add an extra teaspoon of vanilla extract.

→ How long do these blondies stay fresh?

When stored in an airtight container in the refrigerator, these blondies will stay fresh for up to 5 days. You can also freeze them for up to 3 months - just wrap individual portions tightly.

→ Can I add other mix-ins to the blondie batter?

Absolutely! Consider adding chopped nuts like macadamias or almonds, dried cranberries, or even a handful of small marshmallows. Just keep the total amount of add-ins similar to the 150g of white chocolate chips called for in the recipe.

→ Why did my blondies turn out cakey instead of fudgy?

Cakey blondies usually result from overmixing the batter or using too much flour. Fold the dry ingredients gently into the wet mixture just until combined. Also, be sure to melt the butter and sugar together completely for that signature dense, fudgy texture.