Preheat the oven to 375 degrees F. Grease a 9×13 inch baking pan.

In a medium bowl, combine the fresh blueberries and dark rum (or lemon juice). Stir in 1/2 cup granulated sugar and 4 tsp cornstarch. Set aside.

In a separate medium bowl, combine 1/2 cup each of granulated sugar and brown sugar. Stir in flour, baking powder, salt, ground ginger, and ground nutmeg.

Cut in cold butter with a pastry cutter or a fork until the mixture is crumbly. Whisk one egg in a small bowl and stir into the flour mixture.

Press half of the flour mixture into the bottom of the prepared pan. Spread the blueberry mixture over the crust.

Sprinkle the rest of the flour mixture over the blueberries. Bake in the preheated oven for 40-45 minutes, or until the top is light brown.

Left the bars cool on a rack and then place the fridge to chill. This will make the bars easier to cut and remove from the pan.

Makes about 36 squares.