Place your digestive biscuits in a plastic bag and crush them into fine crumbs using a heavy rolling pin. Mix the crumbs with the melted butter in a bowl until they look like wet, golden sand.

Press the buttery crumbs firmly into the bottom and sides of your loose-bottomed flan tin using a large spoon. Make sure the base is even and compact to prevent the crust from crumbling when you slice it later.

Preheat your oven to 180°C and bake the biscuit base for ten minutes until it feels firm and smells toasted. Remove it from the oven and let it cool completely while you prepare the creamy lime filling.

Pour the full-fat condensed milk into a large mixing bowl and add the three large egg yolks very carefully. Whisk them together for about two minutes until the mixture is thick, pale yellow, and very smooth.

Grate the zest of four limes directly into the bowl to capture all the natural citrus oils and aroma. The zest provides a beautiful green speckled look and a very deep lime flavor to your finished pie.

If you enjoy that citrusy brightness in baked goods, you might also love this tangy lime-infused pound cake that uses a similar flavor profile to wonderful effect.

Gradually whisk the fresh lime juice into the condensed milk mixture until it starts to thicken up naturally. The acid in the lime juice reacts with the milk to create a very rich and velvety texture.

Pour the lime mixture over the cooled biscuit base and spread it out evenly using a rubber spatula. Tap the tin gently on the counter to remove any small air bubbles trapped inside the creamy filling.

Place the pie back into the oven at 160°C and bake for fifteen minutes until the filling is set. It should still have a tiny wobble in the very center when you gently shake the baking tin.

Let the pie cool to room temperature before placing it in the refrigerator for at least four hours. Chilling is the most important step to ensure the pie is firm enough to cut into perfect slices.

Whisk the double cream until soft peaks form and pipe or spoon it over the top of the pie. Garnish with extra lime zest or thin lime slices for a very professional and elegant farmhouse look.