Mary Berry Blueberry Traybake

There’s something a bit magic about this blueberry traybake. Maybe it’s the soft sponge that holds the berries like little pockets of jam. Or maybe it’s the mascarpone icing—fluffy, cool, not too sweet, like a pillow for your cake.

I first made this after buying a giant punnet of blueberries on a whim, thinking I’d be the sort of person who snacks on fruit instead of biscuits. That lasted about a day. So, into a traybake they went. First try? I overbeat the batter and dumped in too many berries—ended up with a sponge that looked like a blueberry crime scene.

Second round, I kept things simple. Cold margarine, light mixing, and just enough berries to scatter without sinking. The result was a soft, golden base with bright purple bursts and a cloud of mascarpone on top. It’s the kind of traybake that feels fancy, but forgives a lot.

WHY THIS ONE WORKS SO WELL

Cold margarine straight from the fridge might sound odd, but it’s key here—it helps keep the batter light and stops the cake from feeling greasy. The mascarpone icing isn’t overly sweet, which balances out the sugar in the sponge. And the berries? They don’t just sit on top—they bake into the sponge, giving it a tart, juicy bite that cuts through the richness.

It also holds up beautifully once sliced—doesn’t crumble or weep—so it’s ideal if you’re feeding a crowd, or just want a slice with your mid-afternoon tea for the next few days.

INGREDIENTS + WHY THEY MATTER

Margarine (225g, cold) – Straight from the fridge. Whips up fast and keeps the sponge tender.
Self-Rising Flour (275g) – Handles the lift without faff.
Superfine (caster) sugar (225g) – Dissolves quickly, so you get a soft crumb.
Eggs (4 large) – Room temp if you can manage it—helps everything blend properly.
Milk (4 tbsp) – Loosens the batter slightly for a better texture.
Vanilla Extract (1 tsp) – Gives warmth and depth behind the blueberries.
Fresh Blueberries (225g) – Tart and juicy. Don’t overload or they’ll sink and swamp the sponge.
Mascarpone (250g) – Full-fat only. Light, creamy, and beautifully mellow.
Butter + Icing Sugar (for the frosting) – Helps give the mascarpone structure and sweetness.

MAKING IT YOURS (WITHOUT RUINING IT)

Want it zesty? Add lemon zest to the batter or the icing—it works beautifully with the berries.
No mascarpone? You can use full-fat cream cheese, but it’s tangier. Add a little extra sugar to balance.
Frozen berries? I tested it—they work, but toss them in a bit of flour first and bake 5 minutes longer.

MISTAKES I’VE MADE (AND HOW TO AVOID THEM)

What Went Wrong	Why It Happens	How to Fix It
Sponge was tough	Overmixed the batter	Mix until just combined, then stop
Icing split or curdled	Ingredients too cold or over-whipped	Let everything soften slightly, go slow
Berries all sank	Too many, or didn’t flour them	Use the right amount, scatter evenly

HOW TO MAKE MARY BERRY’S BLUEBERRY TRAYBAKE

1. Preheat Your Oven
   Set to 180°C (160°C fan). Grease and line a 30x23cm traybake tin.
2. Mix the Batter
   Put all sponge ingredients—cold margarine, sugar, flour, baking powder, eggs, milk, and vanilla—into a bowl. Beat until just smooth.
3. Bake
   Spoon into the tin and level. Scatter over the blueberries. Bake for 30–35 minutes until golden and springy.
4. Cool
   Let the cake cool completely in the tin. This helps keep the sponge moist and stops the icing melting.
5. Make the Frosting
   Beat softened butter and icing sugar until fluffy. Add mascarpone and vanilla, mix gently until smooth.
6. Assemble
   Spread frosting over cooled cake. Dot with extra blueberries and cut into 16 neat squares.

TIPS FROM MY KITCHEN

I use a spatula, not a whisk, to mix in the mascarpone—stops it splitting.
If your blueberries are extra juicy, pat them dry with kitchen paper first.
The frosting firms up in the fridge—ideal if you need to transport it later.

STORAGE + SERVING

Keeps: 3 days in the fridge, covered
Freezes: Sponge only—unfrosted slices freeze well for 2 months
Serve with: A mug of coffee, or Greek yogurt for breakfast if you’re feeling cheeky

FREQUENTLY ASKED QUESTIONS

Q: Can I use butter instead of margarine?
Yes—but let it soften first, or it won’t mix properly. Cake may be slightly denser.

Q: Can I make this without icing?
You can. The sponge is lovely on its own. Dust with icing sugar or serve with cream.

Q: Do I need to coat the blueberries in flour?
Not if you scatter them on top. If you fold them into the batter, yes—it helps keep them from sinking.

Try More Recipes:

• Mary Berry Pear and Blueberry Galette
• Mary Berry Blueberry Muffin Recipe
• Mary Berry Petit Fours