Mary Berry Key Lime Tranche

I made this on a Tuesday, thinking I’d save it for the weekend. By Wednesday afternoon, it was gone—half of it eaten straight from the tin with a spoon. To be honest, I didn’t expect something this simple to taste like sunshine in dessert form. But here we are.

The first time I made it, I overmixed the filling and it split slightly—not a disaster, but not the silky set I wanted. Also, I forgot to zest the limes before juicing them. Rookie move. But let me show you how I fixed that—and why I now keep this on standby anytime I need a crowd-pleaser with minimal faff.

Why This One Works So Well

• Most key lime-style recipes call for baking. Not this one. The acid in the limes thickens the condensed milk naturally—no oven required.
• Using full-fat cream cheese and pouring double cream keeps the texture rich but smooth, not stodgy.
• Mary’s proportions are spot on. I tried increasing the lime juice once—just made it soupy. Her version just works.

INGREDIENTS + WHY THEY MATTER

• Full-fat cream cheese – Gives it body and tang. Low-fat turns watery and ruins the set.
• Condensed milk – Adds sweetness and acts like a magic thickener with the lime juice.
• Lime zest + juice – Zest adds brightness; juice is what thickens the filling. Don’t skip either.
• Pouring double cream – Whipped lightly, it gives that cloud-like topping.
• Digestive biscuits – Classic British base. Graham crackers are a decent swap if you’re abroad.
• Butter + demerara sugar – Binds the base and gives it a slight crunch and caramel edge.

Making It Yours (Without Ruining It)

• Gluten-Free: Use GF digestive-style biscuits—I tested with Schär and it held up fine.
• Dairy-Free: Honestly, don’t. I tried it with coconut cream and oat-based condensed milk. It didn’t set and tasted like suntan lotion.
• Want a twist: Add crushed pistachios to the base. I did once—got fancy praise for it.
• No pouring cream: You can use regular double cream, just don’t overwhip it. Pouring cream gives that soft, spreadable finish.

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

What Went Wrong	Why It Happens	How to Fix It
Filling didn’t set	Too much lime juice, overmixed	Use exact juice amount, mix gently
Base was too crumbly	Not enough butter	Weigh ingredients—don’t guess
Cream was grainy	Overwhipped double cream	Stop at soft peaks, not stiff
Forgot zesting limes	Juiced first, couldn’t zest after	Zest before juicing—always

HOW TO MAKE MARY BERRY’S KEY LIME TRANCHE

1. Crush the biscuits – I use a freezer bag and rolling pin for this. Proper crumbs mean better base texture.
2. Mix in melted butter and sugar, press into a 36 x 12.5 cm loose-bottomed fluted tin. Use the back of a spoon to get into the corners. Chill for at least 30 minutes.
3. Beat the cream cheese until smooth—don’t rush.
4. Gradually whisk in condensed milk and zest of 2 limes, then add all the lime juice. It’ll thicken before your eyes.
5. Pour filling into chilled base, smooth it out, and chill for 2 hours until softly set.
6. Whip the cream to soft peaks, spread over the top, and swirl. Sprinkle with remaining zest. Done.

TIPS FROM MY KITCHEN

• I zest the limes straight over the bowl—less mess, more citrus oils.
• My tin is ancient and non-stick’s long gone, so I line it with baking paper strips to lift the slice out.
• If you only have round tins, go for it—it still works, but slice shapes will be rustic.
• I sometimes mix half the cream into the filling and half on top for a lighter set.

STORAGE + SERVING

• Keeps in the fridge for 3 days, though the cream topping can deflate a bit.
• Don’t freeze it. I tried. It went weirdly grainy.
• Best served cold, with fresh raspberries or mint if you’re feeling extra. I once crumbled a leftover shortbread on top and felt like a genius.

FAQs – Real Query Answers

Q: Can I use bottled lime juice?
A: I did once out of desperation. It was flatter, less zingy. Use fresh—it makes all the difference.

Q: Can I use light cream cheese?
A: No. It won’t set the same, and the texture’s off. Full-fat or bust here.

Q: Can I make it ahead?
A: Yes. Up to 24 hours. Just don’t add the whipped cream until just before serving if you want it to stay picture-perfect.

Q: Why is it called a tranche?
A: It’s just a posh word for “slice” or “slab.” Same dessert, fancier name.

Try More Mary Berry Recipes:

• Mary Berry Lime and Polenta Cake
• Mary Berry Lemon Lime Traybake
• Mary Berry Lemon Drizzle Traybake
• Mary Berry Lemon Cupcakes