There’s something effortlessly special about this blueberry traybake. The sponge is soft and golden, the blueberries bake into jammy bursts, and the creamy mascarpone frosting brings it all together with just the right touch of richness.
This recipe was born from a surplus of blueberries I optimistically bought, thinking I’d snack on them instead of biscuits. That lasted a day. So I baked instead. My first attempt was a disaster—overmixed batter, too many berries, and a purple mess. But with a few tweaks—cold margarine, gentle mixing, and a light hand with the fruit—I got it just right. Now it’s my go-to for quick bakes that feel a little fancy without the fuss.
Why You’ll Love It
- Cold margarine keeps the sponge light and moist.
- Blueberries bake into the sponge, not just sit on top.
- Mascarpone frosting is cool and creamy—not too sweet.
- Perfect for slicing and sharing, or keeping for weekday treats.
Ingredients & Their Purpose
For the Sponge:
- 225g cold margarine – Straight from the fridge; helps create a light, tender crumb.
- 275g self-raising flour – No need for extra leavening.
- 225g caster sugar – Fine sugar ensures a soft texture.
- 4 large eggs – Bind the mixture and add richness.
- 4 tbsp milk – Loosens the batter just enough.
- 1 tsp vanilla extract – Adds warm depth of flavour.
- 225g fresh blueberries – Sweet, tart bursts of fruit throughout the sponge.
For the Frosting:
- 100g softened butter – Forms the base of the icing.
- 150g icing sugar – Adds sweetness and structure.
- 250g full-fat mascarpone – Light and creamy with a mellow flavour.
- 1 tsp vanilla extract – Enhances the frosting’s flavour.
Make It Your Own
- Add lemon zest for a fresh citrus twist.
- Use cream cheese instead of mascarpone if needed—just add extra sugar to offset the tang.
- Swap in frozen berries (toss them in flour first and bake a few minutes longer).
- Skip the frosting for a simpler cake—dust with icing sugar or serve with yogurt.
Common Pitfalls (And How to Avoid Them)
| Problem | Cause | Solution |
|---|---|---|
| Tough, dry sponge | Overmixing | Mix just until everything is combined |
| Icing split or curdled | Cold ingredients or over-whipping | Use room temp ingredients and mix gently |
| Sinking berries | Too many or added too early | Scatter a light amount on top just before baking |
How to Make It
1. Prep the Oven & Tin
Preheat to 180°C (160°C fan) / Gas 4. Grease and line a 30x23cm traybake tin with baking paper.
2. Make the Batter
Add margarine, flour, sugar, eggs, milk, and vanilla to a large bowl. Beat everything together until just smooth—don’t overmix.
3. Add the Berries
Pour batter into the tin and level the top. Evenly scatter blueberries over the surface.
4. Bake
Bake for 30–35 minutes until golden and springy to the touch. A skewer should come out clean.
5. Cool Completely
Let the cake cool fully in the tin. This helps the sponge stay moist and stops the icing from melting.
6. Make the Frosting
Beat butter and icing sugar until light and fluffy. Fold in mascarpone and vanilla with a spatula (not a whisk) until smooth.
7. Ice and Slice
Spread frosting over the cooled cake. Top with a few extra blueberries if you like, then slice into 16 squares.
Baker’s Tips
- Use a spatula (not a whisk) to fold in mascarpone—prevents the icing from splitting.
- Pat juicy blueberries dry before baking to avoid soggy spots.
- Chill the frosted cake if transporting—it helps the icing firm up.
Storage & Serving
- Store: In the fridge for up to 3 days, covered.
- Freeze: The sponge (without frosting) freezes well for up to 2 months.
- Serve: With tea, coffee, or even a dollop of yogurt for breakfast.
FAQ
Can I use butter instead of margarine?
Yes—but let it soften first. The texture may be slightly denser.
Can I skip the icing?
Absolutely. The sponge is lovely on its own—try dusting with icing sugar.
Do I have to flour the blueberries?
Only if mixing into the batter. If scattering on top, no need.
Want More Bakes Like This?
- Mary Berry Pear & Blueberry Galette
- Mary Berry Blueberry Muffins
- Mary Berry Petit Fours
