Preheat the oven to 180°C. Lightly grease a 26cm loose-bottomed flan tin.
In a food processor combine ground almonds, sliced almonds, spice, flour, sugar and melted butter and pulse until finely ground and mixture starts to clump together. Press mixture into base of the flan tin. Chill in the fridge for 20 minutes then bake for 10-15 minutes until just lightly golden. Remove from the oven and allow to cool.
Meanwhile, place egg yolks, condensed milk, cornflour, lemon juice and zest in a medium saucepan and mix well. Heat gently, stirring with a wooden spoon, until mixture starts to thicken (about 4-5 minutes). Leave to cool for 20 minutes.
Whisk the egg whites with most of the caster sugar (reserve 1 Tbsp), beating until thick, glossy and white.
Pour lemon mixture into pre-cooked base and pile on the meringue, making sure to bring the meringue right to the edge of the almond shell to seal in the filling. Sprinkle with reserved sugar then bake for 15-20 minutes until meringue is golden and puffed.