Combine the butter, icing sugar and almonds in the mixer. Add the eggs, egg yolk, vanilla pod and salt and mix until homogenous. Add the flour in one go and then mix as little as possible, only enough to be able to shape the dough into a ball. Flatten slightly and refrigerate overnight (or at least 1h30).

Roll out the dough so that it's 3mm thick (or 2mm for mini pies), place in the pie tin and refrigerate again for 1-1h30. This will prevent the dough from shrinking when baking. Blind bake for 20 minutes at 180°C and the let cool on a rack.

Cook all the remaining ingredients (except the butter and the gelatine if you're going to use it) on a low heat. Keep an eye on the exact temperature - the mix should never exceed 85°C (185F) or the eggs might cook.

When the mix starts to thicken, get ready to remove the pan from the heat. How do you know when it's ready? Use the whisk to create a whirl - if the whirl continues to spin for a bit before stopping, you will need to keep it on the heat for a bit longer. If on the other hand it stops immediately, it's ready - you can stop cooking and remove from the heat.

If you want to add gelatine to the mix, do so now.

Strain the lime curd to remove the zests and the basil leaves.

Pour the lime curd into a beaker and let it cool until it reaches about 40-45°C (105-115F). This should take about 5 minutes.

Using a hand-held blender, start mixing the curd at a low speed, then start dropping in the butter and continue to mix until smooth.

Pour the lime curd into the baked pastry and smooth out the mix with a spatula.

Grate some lime zest over the curd and refrigerate for at least 3h if you used the gelatine and 5h if you did not.