Making the dough
Place the cheddar, Parmigiano cheese,
gf flour, dry mustard, salt, cayenne pepper and freshly
ground black pepper in the bowl of a food processor.
Pulse a few times to blend. Add the butter, 1 tablespoon
at a time, pulsing between each addition until the mixture
is the consistency of very small peas. Add the water,
1 tablespoon at a time, and pulse just until the dough
holds together when pinched between your fingers. If
the dough is still too crumbly, add a little more water,
a teaspoon at a time until it reaches the right consistency.