BLACKBERRY AND YUZU MERINGUE PIE

• Plain flour, for rolling • 500g block shortcrust pastry • 4 large egg whites • 225g caster sugar • unwaxed lime, zest • 450g blackberries • 30ml yuzu juice • 4 tbsp cornflour • 325g caster sugar • 100g unsalted butter, cubed • 4 large egg yolks • 1 large egg