In a large bowl, whisk together flour, baking powder, baking soda & salt. With fingertips, cut in cold butter until mixture resembles small peas. In a measuring cup, whisk together water, egg & vinegar. Make a well in dry mixture & pour wet mixture into it all at once. With hands, mix until JUST combined. Roll out pastry & cut 24 squares with a pastry cutter. Fit squares into 24 mini tart pan cups. Set aside in refrigerator until ready to fill.