Step 1: Prepare the Dough

1. In a large bowl, beat the butter, cream cheese, and sugar together until light and fluffy, about 2-3 minutes.
2. Add the egg yolk and vanilla extract, mixing until combined.
3. In a separate bowl, whisk together the flour and salt. Gradually add the dry ingredients to the wet ingredients, mixing until a soft dough forms.
4. Divide the dough in half, shape each portion into a disc, and wrap in plastic wrap. Chill in the refrigerator for at least 1 hour.

Step 2: Prepare the Filling

1. If your jam is very runny, mix it with 1 tablespoon of cornstarch in a small saucepan and heat over low heat until slightly thickened. Let it cool completely before using.

Step 3: Roll Out the Dough

1. On a lightly floured surface, roll out one disc of dough into a rectangle about 1/4 inch thick. Trim the edges to create clean lines.
2. Spread a thin, even layer of jam over the dough, leaving a 1/2-inch border on all sides.

Step 4: Roll and Chill

1. Starting from one of the longer edges, carefully roll the dough into a tight log. Use the edge of the parchment paper or your hands to guide the roll.
2. Wrap the log in plastic wrap and refrigerate for at least 1 hour (or freeze for 30 minutes) to firm up. Repeat with the second disc of dough.

Step 5: Slice and Bake

1. Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
2. Using a sharp knife, slice the chilled logs into 1/4-inch-thick rounds. Place the cookies on the prepared baking sheet, spacing them about 1 inch apart.
3. Bake for 12-15 minutes, or until the edges are lightly golden.
4. Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.

Step 6: Garnish and Serve

1. Dust the cooled cookies with powdered sugar for a decorative touch, if desired.
2. Serve and enjoy with a cup of tea or coffee!