Preheat oven to 400 degrees.

Add flour and salt to a large bowl or food processor. Mix in 1 T. chunks of butter and work together or pulse until well-blended.

Add one tablespoon of water at a time and keep working the dough until all the water has been added.

Form into a large bowl and refrigerate until ready for an hour or until you are ready to use.

Add blueberries, granulated sugar, cornstarch, and lemon zest to a large bowl, set aside.

Lay dough on a floured surface or on wax paper, flatten with your hands first, then roll out with a rolling pin to a large circle.

Transfer the dough to a parchment-lined sheet pan.

Place blueberries in the center of the dough and working in small sections begin to fold the dough from the outer edge to the center, so there is about a two-inch overlap of dough over the berries. There should be a small circle in the middle of uncovered berries.

In a small bowl, beat one egg and then add the milk and beat for another minute.

Brush the egg wash on the dough and sprinkle with coarse sugar.

Bake in a 400-degree oven for 1 hour or until the bottom and top are evenly browned.

Allow to cool for 15 minutes. Serve warm or cold.