Mary Berry’s key lime pie recipe uses a buttery biscuit base, a creamy lime filling made with condensed milk and egg yolks, and a whipped cream topping, and it comes together in under an hour. If you’ve been searching for a foolproof version of this classic, this is the one to bookmark right now.

I made this for the first time on a rainy Sunday afternoon, half-expecting to produce something that tasted like cleaning fluid (because, you know, lime). What came out of the oven was sharp, sweet, silky, and honestly kind of life-changing. Mary Berry never lets us down. Never.

What Makes Mary Berry’s Key Lime Pie Different?

Mary Berry’s version stands out because of its perfectly balanced sweet-tart ratio and the simplicity of the method. She doesn’t overcomplicate it, no water baths, no fancy equipment, no drama.

Most key lime pie recipes float around with varying amounts of lime juice, and getting it wrong means either a pie that tastes like a Chupa Chup or one that makes your face do that involuntary scrunch. Mary nails the balance. IMO, her approach is the gold standard for home bakers.

Ingredients You’ll Need

Here’s everything for one 23cm pie (serves 8)

For the Biscuit Base:

200g digestive biscuits, crushed into fine crumbs
100g unsalted butter, melted
1 tbsp caster sugar

For the Lime Filling:

3 large egg yolks
Zest of 3 limes
150ml freshly squeezed lime juice (roughly 6–8 limes, yes, you’ll be squeezing for a while)
397g tin of sweetened condensed milk

For the Topping:

300ml double cream
1 tbsp icing sugar
Lime zest or thin lime slices to garnish

One thing I’d flag don’t use bottled lime juice. I tried it once out of laziness. The result tasted flat and oddly artificial. Fresh limes are non-negotiable here.

Step-by-Step Method

Step 1: Make the Biscuit Base

Preheat your oven to 160°C (140°C fan/Gas 3). Crush your digestive biscuits into fine crumbs. A food processor works perfectly, or smash them in a zip-lock bag with a rolling pin (oddly satisfying).

Mix the crumbs with melted butter and sugar until the mixture resembles wet sand. Press it firmly into the base and up the sides of a 23cm loose-bottomed tart tin. Press it really firmly; a wobbly base ruins everything. Bake for 10 minutes, then let it cool slightly.

Step 2: Whip Up the Filling

Beat the egg yolks and lime zest together with an electric whisk until the mixture turns pale and thick. This takes about 2–3 minutes. Don’t skip this step, because it’s what gives the filling its silky texture.

Pour in the condensed milk and continue whisking for another 3–4 minutes. Then slowly add the lime juice and mix until fully combined. The filling will thicken slightly as the acid reacts with the condensed milk. Chemistry is kind of amazing sometimes, isn’t it?

Step 3: Bake the Pie

Pour the filling into your cooled biscuit base and bake for 20–25 minutes. You’re looking for a filling that’s set around the edges but still has a very slight wobble in the centre. like a gentle jelly wobble, not a liquid slosh.

Remove from the oven and let it cool completely at room temperature, then refrigerate for at least 2 hours (overnight is even better). Don’t rush this. A warm key lime pie is a sad, messy key lime pie.

Step 4:

Tips for Getting It Perfect

Room temperature egg yolks incorporate better and give a smoother filling. Pull them out of the fridge 20 minutes before you start.
Zest before juicing. Sounds obvious, but I’ve done it the wrong way round more times than I’d like to admit :/
Chill overnight if you can. The flavour deepens and the texture firms up beautifully.
Use a loose-bottomed tin. Getting the pie out of a solid tin without destroying it is a special kind of frustration you don’t need in your life.

Can You Make It Ahead?

Yes, Mary Berry’s key lime pie is an ideal make-ahead dessert. You can bake the whole pie (without the cream topping) up to 2 days in advance and keep it covered in the fridge. Add the whipped cream topping just before serving.

FYI, you can also freeze the baked pie base and filling (without the cream) for up to 1 month. Thaw overnight in the fridge and top with fresh cream before serving.

Common Mistakes to Avoid

A few things that can go wrong and how to dodge them:

Over-baking the filling: If it puffs up and cracks, it’s gone too far. Pull it out at that gentle wobble stage.
Soggy base: Make sure your biscuit base is properly baked and cooled before adding the filling. Adding wet filling to a warm base = disaster.
Too little lime: Don’t reduce the lime juice to be “safe.” The tang is the whole point of this pie.
Skipping the chill time: The pie needs those hours in the fridge to set properly. Patience is a genuine ingredient here.

Why This Recipe Works Every Time

The combination of condensed milk and egg yolks creates a filling that sets firm without needing gelatine or cornflour. The acid in the lime juice essentially “cooks” the condensed milk, which is why the baking time is relatively short.

Mary Berry’s genius here is trusting the science. She keeps the ingredient list tight, the method clean, and the result is a pie that looks impressive but requires zero professional skill. That’s the sweet spot for home baking.

Final Thoughts

Whether you’re making this for a dinner party, a summer gathering, or purely for yourself on a Tuesday evening (no judgment), this recipe delivers every single time. The balance of that crisp, buttery base with the sharp, creamy filling is genuinely hard to beat.

Give it a try this weekend, and if it disappears before you’ve even added the cream topping, you’ll know you’ve nailed it. Happy baking!