In a medium-sized saucepan, whisk together the sugar, cornstarch, and salt.

Add the water and lemon juice and stir. Add the blueberries and butter. Stir. Heat on medium-low heat until the sugar starts to melt. Then turn the heat to medium and let the blueberry mixture simmer for about 5 minutes or until it thickens a little. Remove from the heat and add the vanilla and stir to mix well. Let the mixture cool while you prepare the crust.

Preheat the oven to 400 degrees F.

Roll one crust to 12 inches round and place it on a baking sheet with a sheet of parchment paper underneath. Set aside.

To the second crust, spread the blueberry powder over the crust. Fold the crust over itself and start kneading the dough to work the blueberry powder into it and color it purple. Add additional blueberry powder if necessary unless it reaches the desired color. Then roll out the crust to approximately 12 inches and 1/8-inch thick.

Cut flowers out of the purple crust by using a 2-inch cookie cutter. Cut 5 circles and lay them out in a row overlapping each circle with the next dough circle. Cut the circle row in half lengthwise. Roll up one row into a tube to form a rose. Gently pull the petals downward to separate the petals and open up the rose. Cut off any excess dough from the bottom of the flower. Repeat with the other half of the circle row. Continue making roses until you have several for decorating. Set the flowers aside. Make a dough ball of all the leftover scraps.

Roll out an 8 x 2-inch long strip of dough. Cut four 1/2-inch wide strips. Cut these strips in half. Start with one end of a strip and roll up the dough into a tube to form a bud. Handshape if necessary and cut off any excess dough at the bottom of the bud.

Pour the cooled blueberry mixture in the middle of the 12-inch pie crust, leaving a 2-inch border all the way around the crust.

If the pie crust edges of the crust are thin, fold over a 1/4-inch hem all the way around the galette. Then fold up the crust all the way around the galette overlapping the blueberries a little.

Place the flowers around the galette edges in a pleasing arrangement.

Brush the crust and flowers with the egg.

Bake for 30 to 40 minutes or until the crust is cooked through and flaky. If the crust starts to over-brown before the cooking time is finished, place a sheet of aluminum foil loosely on top.