1. First make the dough. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt, and set aside. Using an electric mixer beat the Plugrá Butter on medium-high speed for 30 seconds. Reduce the speed to medium and add the sugar gradually, beating until light and fluffy. Add the mascarpone cheese and the egg, and beat until evenly mixed. Scrape the bowl and add the flour mixture on low speed, mixing until the flour is completely blended in. Scrape the bottom and sides of the bowl and give the dough a few stirs to be sure it is completely mixed. Divide the dough into two equal parts, form each part into a flat rectangle, and wrap each one with plastic wrap. Chill for 2 hours, or until the dough is firm enough to handle.
2. Next, make the filling. Combine the sugar and the espresso powder, set aside. Melt the Plugrá Butter, set aside.
3. Work with one part of the dough at a time. Roll the flattened rectangle between two sheets of wax paper or parchment until it measures 11 x 8-inches. Refrigerate the rolled dough while you roll the remaining portion of dough. Trim the edges of both rolled rectangles, and brush each with the melted Plugrá Butter. Sprinkle 2-1/2 tablespoons of the espresso-sugar mixture evenly over each rectangle. (Reserve the remaining espresso mixture.) Starting at a short edge, roll each rectangle up snuggly, jellyroll style. Pinch the seams to seal and wrap each log in plastic wrap. Chill for 4 hours, or until firm.
4. Preheat a conventional oven to 375ºF. Position an oven rack in the center of the oven. Divide the reserved espresso mixture into two parts. Sprinkle one part on a work surface and roll one of the logs in the mixture, coating completely. Repeat with the remaining log. Cut the logs into 1/4-inch slices using a thin, sharp knife. Place the pinwheels 1 inch apart on ungreased baking sheets. Bake one sheet at a time until the edges are firm and light golden brown, reversing the pans halfway through the baking time, about 8 to 10 minutes. Cool the cookies on the pan for 1 minute, then transfer to wire racks to finish cooling.
5. Lastly, prepare the garnish. Melt the chocolate in a double boiler or in the microwave. Place a piece of wax paper or parchment under the wire rack and drizzle the melted chocolate over the cookies using a fork that has been dipped in the chocolate, or place the chocolate in a zippered plastic bag, snip a small opening in a corner of the bag, and squeeze the chocolate over the cookies. Refrigerate for a few minutes to let the chocolate set.
6. Store in an airtight container with wax paper between each layer of cookies.