Combine all-purpose flour, icing sugar, unsalted butter, and lemon zest in a mixing bowl.

Rub the mixture between your fingertips until it resembles fine crumbs.

Add egg yolk and salt to the crumb mixture.

Knead briefly until a smooth dough forms.

Wrap the dough and refrigerate it for 60 min.

Preheat the oven to 170°C / 340°F.

Roll the chilled dough to a 3 mm thickness.

Line the tart pan with the rolled dough.

Cover the crust with parchment paper and fill it with pie weights.

Bake the crust for 20 min at 170°C / 340°F.

Remove the pie weights and bake the crust for 5 min more.

Combine 150 g blueberries, 2 tablespoons granulated sugar, and lemon juice in a saucepan.

Cook the blueberry mixture for about 10 min until thickened.

Cool the blueberry compote and spread it over the baked crust.

Freeze the filled crust for 15 min.

Soften gelatine sheets in cold water until flexible.

Heat heavy cream and granulated sugar until the sugar dissolves and the cream reaches a boil.

Add blue matcha powder and drained gelatine sheets to the hot cream.

Blend the panna cotta mixture for a few seconds with the immersion blender held at the bottom.

Stir Greek yogurt into the blue panna cotta until smooth.

Cool the panna cotta until no longer hot, then pour it over the chilled blueberry layer.

Refrigerate the tart for about 180 min until the panna cotta is set.

Decorate the tart with edible flowers and additional blueberries if desired.