Preparation

• Scoop up a generous teaspoonful (2 level teaspoons) of the dough and shape it into a 1-inch ball with your hands. Roll the ball in the sugar and set it on a tray lined with waxed paper. Repeat with the rest of the dough, setting the balls slightly apart. Press a thumb or forefinger, dipped in flour, into each ball to create a depression. Cover and refrigerate the cookies for at least 2 hours, but preferably overnight.

• Remove the cookies from the refrigerator and arrange them 1 inch apart on an ungreased or foil-lined cookie sheet. Position a rack in the center of the oven and heat the oven to 325°F. Let the cookies sit at room temperature while the oven heats. Bake the cookies for 10 minutes. Gently redefine the depressions with your thumb or the tip of a wooden spoon’s handle, if necessary. Rotate the sheet and continue to bake until the tops are lightly colored and the bottoms are golden brown, another 8 to 12 minutes. Transfer the cookies to a rack and let cool completely.

• When the cookies are cool, prepare the filling: Put the chocolate and butter in a heatproof bowl set in a wide skillet of almost simmering water, or in the top of a double boiler. (Or microwave on medium power for 1 to 2 minutes, stirring after the first minute.) When the chocolate is almost completely melted, remove the bowl from the heat and stir until completely melted and smooth.
• Usine a spoon, fill the depression of each cookie with the chocolate filling. If the filling hardens while using, reheat it in the pan of hot water.