8 oz. bittersweet or semi-sweet chocolate, cut into bits
3 oz. sweet butter, cut into pieces
1 egg yolk
1/2 c. unsweetened cocoa powder

Line the bottom and sides of a 5 x 9 inch loaf pan with parchment, waxed paper or foil. Melt the chocolate with the butter and 1/4 cup water in a bowl set in a barely simmering water bath. Stir from time to time until the mixture is melted and smooth. Or, microwave on medium power (50 percent), stirring once or twice, for about 2 minutes. Off heat, whisk in the egg yolk just until incorporated. Do not beat or mix more than necessary. Strain truffle mixture into the lined pan and chill, without stirring, until firm, about 1 hour.

Remove pan from refrigerator. Unmold and cut into 3/4 inch squares. (If chocolate is too firm to cut without breaking, wait 15 to 20 minutes to soften slightly.)

Put cocoa in a shallow dish. Roll truffle squares in cocoa, rounding them between the palms of your hands. Dust your hands with cocoa as necessary to keep truffles from sticking. If the truffles are too firm to shape, wait until they soften slightly. If they are too soft, refrigerate briefly. Shake truffles gently in a dry strainer, if necessary, to remove excess cocoa.

Truffles may be made and stored in an airtight container in the refrigerator for 10 days or frozen for up to 3 months. Bring to room temperature for serving. Makes about 30 small truffles.