For the shortcrust pastry base:
1) Preheat the oven to 210C/Gas 7. Sift the plain flour into a mixing bowl and, using a pastry blender, blend in the chilled butter until the mixture resembles coarse meal. Add the caster sugar, egg yolks, salt and water. Mix to a soft dough.
2) Roll out the pastry on a lightly floured surface and use to line a deep 23cm tart dish or 22cm fluted flan dish sprayed with cooking spray. Prick the bottom and chill.
3) Trim off any excess pastry from around the edge of the shortcrust base. Line the tart shell with baking paper and fill with dried beans or rice to weight down the pastry.
4) Bake the shell for 10 minutes. Remove the paper and beans/rice and return to the oven for 10 more minutes. Cool.
For the filling:
1) Lower the oven temperature to 180C/Gas 4. Beat the egg yolks in a large bowl until light and creamy. Beat in the condensed milk then add the lime zest and juice. Mix well and continue to beat until the mixture is thick.
2) In a separate bowl, beat the egg whites until they form stiff peaks. Slowly add the caster sugar until just combined. Gently fold into the lime mixture.
3) Pour the lime filling into the baked shortcrust shell.
4) Bake for 20 to 25 minutes or until filling is set and begins to brown. Remove and cool, then chill in refrigerator.
For the topping:
1) Before serving, whip the double cream, icing sugar and vanilla essence. Either spoon the cream directly onto the tart or into an icing bag, to decorate the edges.
2) Cut the lime slices from the centre to the edge and twist. Arrange the lime between dollops of whipped cream.
3) Lightly sprinkle with lime zest and decorate with mint leaves; serve.