Chocolate Pinwheel Cookies

Sift together the flour, salt, and baking soda. Set aside.

Break or chop the bittersweet chocolate into 1-inch pieces. Melt the bittersweet chocolate pieces in the top of a double boiler or in a heatproof bowl, over barely simmering water, stirring occasionally until smooth. Set aside.

In a large bowl, cream the butter with an electric mixer on medium-to-low speed until smooth, about 2 minutes. Mix in the sugar and beat for an additional 2 minutes. Add the egg and vanilla, mixing well until combined. Reduce the speed to low and add the flour mixture in two additions, mixing until just incorporated.

Separate out 2 cups of the dough and set aside.

Dissolve the espresso powder in the boiling water and set aside to cool. Once cool, mix the espresso and cocoa into the remaining dough until the dough is uniformly colored. On low speed, add in the melted chocolate, mixing until thoroughly combined.

Divide each flavor of dough (vanilla and chocolate) into three equal pieced. On Pieces of plastic wrap, shape each piece of dough into a 5-inch by 5-inch square and wrap well. Note: The chocolate dough may be thicker than the vanilla.

Chill the dough for at least 30 minutes in the refrigerator.

While the dough is chilling, tear off twelve 10-inch squares of parchment paper. Roll each piece of chilled dough into thinner 7-inch by 7-inch squares between two pieces of parchment paper. Without removing the parchment paper, layer the dough on a baking sheet and chill in the refrigerator for about 15 minutes.

While chilling, tear three 13-inch sheets of plastic wrap. To form the pinwheels, remove one square of the chocolate dough and one square of the vanilla dough from the refrigerator, peeling off the top sheet of paper from each. Invert the vanilla squares on top of the chocolate square (or vice versa, as desired). Trim the edges to make a neat square. Gently roll over the dough with a rolling pin to seal both doughs together. Peel off the top layer of parchment paper. Starting with the edge of the dough nearest you and using your fingertips, slowly curl the edge of the bottom layer of dough up over the top layer, so there is no space in the center of the pinwheel. Continue rolling the dough tightly, jelly roll-style. Use the parchment paper to help you roll the dough into a cylinder. After you form the cylinder, roll it gently back and forth on a flat surface to extend its length somewhat. Put the elongated cylinder on a cut piece of plastic wrap, and starting with the edge nearest you, roll it tightly and twist the ends of the plastic to seal. The dough should be between 8 and 9 inches long and 1 1/2 inches thick. Refrigerate the dough cylinder, and repeat the above procedure with the remaining four pieces of dough.

Allow the cylinders to chill for about 3 hours.

Preheat the oven to 350ºF. Line two cookie sheets with parchment paper.

Slice into ¼-inch rounds and place 1 inch apart on the prepared baking sheet.

Bake for 12 to 13 minutes, making sure not to brown the edges too much. Remove the cookies from the oven, and let stand for 1 minute.

Transfer to wire racks and let cool completely. Store in an airtight container at room temperature for up to a week.