In a medium saucepan, combine the blueberries, lemon zest, juice and sugar and bring to a boil over medium heat.

Mix together the cornstarch and water then stir it into the blueberries.

Turn the heat down so the mixture is just simmering.

Simmer stirring every so often for about 10 minutes until the blueberries have softened and the liquid has thickened. Draw a line across the back of your spoon and the line should hold.

Remove from heat and allow to cool completely

Place the butter, flour, sugar and salt in a food processor and pulse until it looks like lumply sand. Add the ice water 1 tablespoon at a time and pulse between each until the dough just starts clumping together. Don't add more water than you need.

Turn the dough out onto a sheet of baking paper and just gently pull it together – don’t knead it too much as you want it to stay cold for it to become flaky.

Shape the dough into a rough square, then cut in half. Wrap each piece up separately and chill for at least 45 minutes.

Cut the dough in half. Return one half of the dough to the fridge.

Trim it to make straight sides and cut 8 smaller about 2.5 x 4 inches each. Reroll the offcuts to make another 2. Place them all on a baking tray and back into the fridge.

Repeat with the other piece of dough.

Hold back about 1 tablespoon of the filling if you'd like to use it for decorating.

Use your finger to brush a line of water around the edge, then top with another rectangle of dough. Use a fork to crimp the sides firmly all the way round.

Beat together the egg yolk with a dash of water and brush over the tops. Pierce two small slits with a sharp knife.

Place them on the prepared baking trays and bake for 25-27 minutes, turning at the halfway point, until golden and crisp.

Sift the powdered sugar and cinnamon into a medium bowl, then mix in the milk. Adjust the consistency so that it settles after about 10 seconds when stirred - powdered sugar will make it thicker, milk or water to thin it.

For purple icing: push the reserved blueberry filling through a strainer and use the juice to colour the icing.

For the blueberry dots: use the juice from straining the filling as above and dot it onto the tarts with a toothpick, then run the toothpick through the middle of the dots to make swirls.