Combine the cheeses, garlic powder, butter, and salt in a mixer using the dough paddle. The dough will be very crumbly.
Mix in the flour and slowly add in the water (make sure you use very cold water!) until the dough is the consistency of a pie dough.
Divide the dough into halves and form into discs. Wrap in plastic wrap and place in the fridge for at least 30 minutes.
Preheat oven to 375 F.
Place dough on parchment paper or silicon mat and roll out to a 1/8" thickness. Try to make the dough as square as possible. Using a pastry wheel, cut the dough into 1" squares. Poke a hole in the center of each square with a toothpick and transfer to un-greased baking sheets.
Bake 10-15 minutes or until puffed up and golden brown. Remove to cooling racks and sprinkle with additional salt if desired.