Preheat the oven to 200°C.
Line six 10cm tart cases with puff pastry and chill in the fridge for 30 minutes.
Prick pastry bases, line with baking paper and beans, and bake blind for 15 minutes.
Remove paper and beans then bake for 5 to 8 minutes until golden.
Simmer pears, lemon zest, juice, and sugar in water for 10 to 12 minutes until tender.
Boil milk with vanilla seeds in a pan.
Whisk egg yolks, sugar, and cornflour together in a bowl.
Pour boiling milk onto the egg mixture, whisk, and return to the pan to boil while stirring.
Remove the thickened custard from heat and let cool.
Whip double cream with pear liqueur until soft peaks form.
Gently fold the whipped cream into the cooled custard.
Warm the apricot jam with a little water in a saucepan.
Fill the tart cases with the Poire William cream.
Slice the poached pears, fan them out, and place on top of the cream.
Brush the warm apricot sauce over the pears.
Garnish each tart with a mint sprig to serve.