Anna Louise Key lime pie is one of those American classics that translates completely and immediately to British taste — the sharp, vivid lime against the sweetened condensed milk, the buttery digestive base, and the cloud of whipped cream that gives the whole thing a richness and a contrast that is one of the finest dessert combinations I know.
The filling is a specific technique — lime juice and condensed milk with egg yolks, which sets in the oven without any additional gelatine or thickening agent.
The acid in the lime juice reacts with the proteins in the condensed milk and egg yolks during baking to give a silky, slightly creamy, precisely set filling that cannot be replicated by any other method. It is both the simplest filling I make and one of the most perfectly calibrated.
The lime must be vivid and fresh. Bottled lime juice gives a flat, slightly artificial result. Fresh limes — used generously — give the filling its vivid, sharp, completely unmistakable character. I use the zest of the limes as well as the juice for maximum lime fragrance throughout.
Ingredients for Mary Berry Key Lime Pie
For the Biscuit Base
- 250g digestive biscuits, crushed to fine crumbs
- 125g unsalted butter, melted
- 1 tbsp golden caster sugar
- Pinch of fine salt
For the Key Lime Filling
- 4 large egg yolks
- Finely grated zest of 6 unwaxed limes
- 200ml freshly squeezed lime juice — from approximately 8 to 10 limes
- 2 x 397g tins sweetened condensed milk
To Finish
- 300ml double cream, cold
- 2 tbsp icing sugar
- 1 tsp vanilla extract
- Finely grated zest of 2 unwaxed limes — scattered generously over the cream
- Thin slices of lime arranged over the cream
How to Make Mary Berry Key Lime Pie
Step 1 — Make the Biscuit Base
Combine the crushed digestive biscuits, melted butter, caster sugar, and salt. Press very firmly and evenly into a deep 23cm loose-bottomed tart tin or springform tin — using the flat base of a glass to compact the base and a spoon to press the sides. The base must be compacted completely — no loose crumbs.
Refrigerate for 30 minutes while the oven preheats.
Step 2 — Preheat
Preheat your oven to 160°C / 140°C fan / Gas 3.
Step 3 — Make the Lime Filling
Whisk the egg yolks and lime zest together with an electric hand whisk for three to four minutes until the mixture is very pale, thick, and the zest has completely fragmented into the yolk — releasing its essential oils throughout.
Add both tins of sweetened condensed milk. Whisk briefly until combined.
Add the freshly squeezed lime juice. Fold in gently — the mixture will thicken slightly as the acid in the lime juice reacts with the condensed milk. This is the beginning of the setting process.
Step 4 — Fill and Bake
Pour the lime filling over the chilled biscuit base — it should fill the tin generously, coming to within 5mm of the top.
Bake for 20 to 25 minutes until the filling is just set — firm at the edges with a very slight wobble remaining in the centre. The filling should look set but not puffed or cracked.
Cool completely at room temperature — at least one hour. Refrigerate for a minimum of four hours — overnight is considerably better. The filling continues to firm during refrigeration and gives its best texture after a full night in the fridge.
Step 5 — Decorate and Serve
Whip the cold cream, icing sugar, and vanilla to soft, billowy peaks.
Spread or pipe the whipped cream generously over the surface of the set lime filling. Scatter the extra lime zest over the cream. Arrange thin slices of lime decoratively over the top.
Slice with a hot, dry knife — wiped between each cut for the cleanest possible slices.
My Top Tips For Perfect Mary Berry Key Lime Pie
Use freshly squeezed lime juice — not bottled. Fresh lime juice gives a vivid, sharp, completely specific lime character. Bottled lime juice gives a flat, slightly artificial flavour that does not do justice to this filling. Eight to ten limes for 200ml of juice is correct — squeeze them generously.
Whisk the egg yolks and zest together for three to four minutes. This step releases the essential oils from the lime zest into the egg yolks and gives a filling that tastes more intensely, more completely of lime than one where the zest is simply stirred in. The mixture should be visibly pale and thickened before the condensed milk goes in.
The filling sets by acid reaction — not by gelatine or excessive baking. The lime juice reacts with the condensed milk and egg yolks to give the set — do not be tempted to bake it longer to firm it. Over-baked key lime pie filling cracks and gives a slightly rubbery texture. The slight central wobble when it comes out of the oven is correct.
Refrigerate overnight for the best texture. A key lime pie refrigerated for four hours gives a firm filling. One refrigerated overnight gives a silky, perfectly calibrated filling that slices completely cleanly and holds its shape on the plate. Overnight is always better.
The lime zest scattered over the cream is the visual and flavour finishing detail. Finely grated lime zest scattered generously over the whipped cream gives both a vivid green visual contrast and an additional fresh lime fragrance that makes the finished pie smell as good as it tastes. Do not skip it.
Serving Suggestions
Cold from the fridge — key lime pie must always be served cold. In generous slices with extra cream alongside. As a dinner party dessert made entirely the day before — it requires no last-minute work at all.
How to Store Mary Berry Key Lime Pie
In the fridge: Store covered for up to 3 days. The filling stays silky and the base stays crisp throughout.
In the freezer: Freeze without the cream topping for up to 2 months. Defrost overnight in the fridge. Apply the whipped cream fresh before serving.
Mary Berry Key Lime Pie Recipe
Ingredients
Method
- Combine biscuit crumbs, melted butter, sugar, and salt. Press very firmly into a deep 23cm tin. Refrigerate 30 minutes. Preheat oven to 160°C / 140°C fan / Gas 3.
- Whisk egg yolks and lime zest 3–4 minutes until very pale and thick. Add both tins of condensed milk — whisk briefly. Fold in lime juice gently — mixture will thicken slightly.
- Pour over chilled base. Bake 20–25 minutes until just set with a slight central wobble. Cool completely at room temperature. Refrigerate 4 hours minimum — overnight ideal.
- Whip cold cream, icing sugar, and vanilla to soft peaks. Spread or pipe over set filling. Scatter lime zest. Arrange lime slices. Slice with a hot dry knife.
Notes
Frequently Asked Questions
Can I use lemon juice instead of lime?
Yes — lemon juice gives a slightly less sharp, slightly more familiar citrus result. Use the zest and juice of six to eight unwaxed lemons. The method is identical. The result is a lemon version of the same filling — equally wonderful.
Can I make this without baking the filling?
The baking step is what sets the egg yolk proteins and gives the silky, firm texture. Without baking, the filling may not set sufficiently cleanly. The twenty-five minutes at the low temperature is not intimidating and the result is completely reliable.
Can I use a pastry case instead of a biscuit base?
Yes — a blind-baked sweet shortcrust pastry case gives a more elegant, more patisserie-style result. Use the sweet shortcrust pastry recipe on this site. Fill and bake as directed.
Why is my filling not setting?
Either the baking time was insufficient, the oven temperature was too low, or the lime juice quantity was not sufficient to set the condensed milk. Ensure the lime juice is fresh, the oven is properly preheated, and the filling bakes for the full twenty to twenty-five minutes.
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