Put the flour, salt, cayenne, and baking powder in a food processor. Pulse to combine. Add the butter and pulse again until the butter is in small pieces, six to eight 1-second pulses. Add the cheeses, pulse, and finally, add the egg and pulse until the mixture just starts to come together.
Dump the dough on an unfloured surface. If you’re using nuts, sprinkle them on the pile of dough. Knead by lightly smearing the ingredients together as you push them away from you with the heel of your hand until the dough is cohesive. Shape the dough into a flat disk, wrap in plastic, and chill for an hour or two to let the butter firm.
Position racks in the top and bottom thirds of the oven. Heat the oven to 400°F. On a lightly floured surface, roll out the dough to about 1/4 inch thick. Stamp out shapes or cut shapes with a knife. Arrange 1-inch apart on two ungreased baking sheets. Reroll scraps once and stamp again.
Brush with the glaze and sprinkle lightly with kosher or sea salt. Bake until golden brown and thoroughly cooked inside, about 14 minutes, rotating the sheets from front to back and top to bottom about halfway through. To test, break one in half and look to see if the center still looks doughy. If so, cook for a few more minutes, but be careful not to overbake. Let cool on a rack and store only when completely cool.
nutrition information (per serving):
per cracker, Calories
5, Fat Calories
45, Saturated Fat
2, Monounsaturated Fat
4, Polyunsaturated Fat
Photo: Scott Phillips