Preparing the Dough: In a large mixing bowl, commence by creaming together the softened butter and cream cheese until the mixture is smooth and well-combined. Gradually incorporate the sifted flour and kosher salt into the creamed mixture, continuing to mix until the ingredients coalesce into a cohesive ball of dough.
Shaping and Chilling the Dough: Transfer the dough onto a clean surface and gently shape it into a flattened disc. This particular shape facilitates easier rolling. Encase the disc in plastic wrap and refrigerate for 30 minutes, allowing the dough to firm up which aids in rolling.
Rolling Out the Dough: After chilling, liberally flour a flat surface and place the dough upon it. Dust the dough with additional flour and roll it out into a rectangle measuring approximately 10 inches by 12 inches. Subsequently, apply more flour to the dough, and utilize the rolling pin to further roll the dough into a larger rectangle, approximately 10 inches by 30 inches.
Adding the Jam and Forming the Log: Spread the raspberry jam evenly across the surface of the dough, leaving a half-inch margin along one of the shorter edges uncoated. This margin will assist in sealing the dough when rolled. Carefully roll the dough into a log, beginning from the jam-covered end, and align the unjammed edge last to seal the log. Place the log in the refrigerator for an additional 15 minutes to solidify.
Preheating and Slicing the Dough: Preheat your oven to 375 degrees Fahrenheit. Remove the chilled log from the refrigerator, and using a piece of sewing thread or a sharp knife, slice the log into 1/4-inch thick cookies.
Baking: Arrange the cookies flat on a parchment-lined baking sheet, ensuring they do not touch each other. Bake in the preheated oven for 17 to 20 minutes, or until the cookies are lightly golden around the edges.
Cooling and Finishing: Once baked, remove the cookies from the oven and transfer them to a wire rack to cool. After the cookies have cooled completely, dust them with powdered sugar before serving.