Slide a slice of your favorite ice cream between a couple of these thin, crisp chocolate wafers. A summer delight!
Using an electric mixer, cream the butter, gradually adding the brown sugar. Add the egg, beating until fluffy. Blend in the vanilla.
Sift flour, cocoa, baking soda, and salt into a bowl. Mix the dry ingredients into the creamed in several stages, until the dough is uniformly smooth. Cover the dough and refrigerate for 15 minutes. Preheat oven to 350 degrees F and grease two cookie sheets.
Using floured hands, gently roll dough into 1-¼-inch balls. Place the balls onto the cookie sheets, leaving about 3-½ inches between each one. Bake for 15 minutes. Cool cookies on the sheets for 2 minutes, then transfer to a rack to cool completely.
About 30 minutes before assembling the cookies, remove the ice cream from the freezer and place it into the refrigerator to soften slightly. To make the cookies, slide the ice cream out of the carton (or peel away the cardboard). Slice through the ice cream to make rounds about ¾ inch thick. (Use a knife rinsed in hot water.) Sandwich the ice cream between two cookies. Serve at once, or place onto baking sheets and freeze until serving.