In a bowl, whisk together flour, baking powder & salt. Cut in butter until it resembles small peas. In a 1/2 cup measure, place 1 tsp vinegar & fill it nearly to the top with ICE water. Pour the mixture all at once over the flour mixture, mixing quickly, until dough pulls away from sides of the bowl. This should only take a couple of minutes; DO NOT OVER MIX PASTRY. Wrap in plastic wrap & place in fridge until ready to roll out.