To make the filling, put the blueberries in a medium bowl and mix in the flour and sugar and set aside.
To make the dough, put the flour, sugar, butter and salt in a food processor or electric mixer fitted with paddle attachment. Mix on low speed until mixture resembles coarse breadcrumbs.
Add the egg yolk and cold water. Continue to mix on low until a dough forms. Gather the dough together and form it into a disc. Wrap it in plastic wrap and refrigerate for 15 minutes.
Preheat the oven to 180 C and line 2 baking trays with parchment paper.
Take the dough out of the fridge and divide it into 4 portions (or 6 portions if you want little tarts).
On a lightly floured surface, roll out each portion of dough until it is quite thin, about 3-4mm. Pace the rounds of dough onto the baking trays.
Put 3-4 large tablespoons of Georgia blueberry filling in the centre of each tart, leaving a 4cm border around the edges.
Roughly fold in the edges of the dough so it overlaps and covers only some of the strawberry filling.
Bake for 30-35 minutes, until the pastry is golden.