Instructions

• Preheat oven to 350°F.
• Set up a double boiler or place a heatproof bowl over a pot of simmering water. Put the chocolate chips, sweetened condensed milk, and shortening in the top of the double boiler or bowl. Stir until melted and smooth. Remove from heat and let cool slightly until spreadable but not hot.
• In a large bowl, use an electric mixer to beat the butter, brown sugar, vanilla extract, and salt until creamy and well combined.
• Measure 2 cups all-purpose flour and sift it. Add the sifted flour to the butter mixture and mix until a crumbly dough forms. Add a few drops of milk, as needed, and mix just until the dough comes together into a non-sticky blob.
• Divide the dough into three equal portions.
• On a lightly floured surface, roll each portion into a 10 x 6-inch rectangle.
• Spread the chocolate filling evenly over each rectangle, leaving a small border along one long edge. If using nuts, sprinkle the 3/4 cup chopped walnuts or almonds over the filling.
• Starting at a 10-inch side, roll each rectangle up tightly into a log. Use a wide metal spatula or turner to help lift and transfer each roll seam-side down to an ungreased cookie sheet.
• Bake the cookie logs 20 to 25 minutes, or until they are light golden brown.
• Remove from the oven and let cool slightly on the cookie sheet until firm enough to move without falling apart. Dust the tops with powdered sugar and allow the logs to cool completely. Wrap in saran wrap or plastic wrap to store.
• To serve, cut the cooled logs into slices about 1/4-inch thick. The whole rolls can be frozen; defrost before slicing.