Mexican Chocolate Icebox Cookies

From Maida Heatter's Book of Great Chocolate Desserts

1 1/2 cups sifted flour
3/4 cup unsweetened cocoa powder (variant: 100g cooking chocolate - thanks Trevor!)
1/4 teaspoon salt
generous pinch black pepper
generous pinch cayenne
3/4 teaspoon cinnamon
6 oz sweet butter (unsalted; 3/4 cup; margarine will do)
1 cup granulated sugar
1 1/2 teaspoons vanilla extract
1 large egg

Sift together flour, cocoa, salt, pepper, cayenne and cinnamon and set aside.

(I do the following process all in the food processor).
Cream the butter, add the sugar and vanilla and mix thoroughly. Beat in the egg, the gradually add the dry ingredients until all mixed (scrape down processor regularly).

Turn the dough onto a lightly floured board. Shape the dough into a cylinder about 10 inches long and 2 inches in diameter (I divide the dough in two so it's easier to ship about).

Wrap the cylinder of dough in wax paper (or bake/lunch paper - there's enough butter it won't really stick) and place in the freezer until firm. Or it may be kept frozen. (This is so it's easier to cut. You *can* leave it too long so it goes totally solid and is nigh on impossible to cut - I did that the last time, but you just move to a bigger heavier knife, or wait until it all thaws a bit.) Before baking, preheat the oven to 375F (190C, or 150 if your oven is fan-forced).

Unwrap the dough, placing it on a board. With a sharp heavy knife, cut it into slices 1/4 inch thick. Place on cookie sheets (they pretty much don't spread at all).

Bake 10-11 minutes, reversing the sheets top to bottom, back to front once during baking to ensure even browning. The cookies are done when they are almost firm to touch - don't leave 'em too long as it's impossible to see if they're burning.

Let them cool for a few seconds on the sheets until firm enough to be moved. With a wide metal spatula, transfer the cookies to racks to cool.

Store airtight.