Prepare the blueberry puree by blending fresh blueberries in a food processor until smooth. Combine with caster sugar and water in a saucepan, cook over medium heat until thickened, about 5-7 minutes. Let cool completely.

Make the pastry by whisking together plain flour, icing sugar, ground ginger (if using), and salt. Cut in cold unsalted butter until crumbly. Add egg yolk and cold water, mix until a dough forms. Chill wrapped in cling film for 20 minutes.

Roll out the pastry on a floured surface to about 4mm thickness and transfer to a greased tart tin. Trim excess and prick the base to prevent bubbling. Chill again for 20-30 minutes.

Preheat your oven to 190°C (fan). Line the pastry with baking paper and add weights. Bake for 15 minutes until golden at edges. Remove weights and bake for another 5-10 minutes until golden brown.

Prepare the lemon filling by whisking egg yolks, condensed milk, lemon juice, lemon zest, and salt until smooth.

Once cooled, pour the lemon filling into the baked pastry and swirl the cooled blueberry puree on top for a marbled effect.

Bake the assembled tart for 15 minutes until the filling is set but still slightly wobbly. Cool at room temperature for 30 minutes, then chill in the fridge.

Garnish with fresh blueberries and lemon slices before serving.