1. Arrange a large piece of plastic wrap on the counter. Using a rolling pin, roll out the puff pastry on the plastic into a 10 × 13-inch rectangle. Sprinkle the top and bottom often and generously with the confectioners sugar to prevent sticking (you won’t use it all). Using an offset spatula, spread the jam evenly over the dough to within ¼ inch of the edges.

2 Cut the dough in half lengthwise (you’ll have two 5 × 13-inch rectangles}, Starting on one long side and using the plastic as a guide, roll up the dough jellyroll style. Pinch the seam to the roll so it sticks together. Repeat with the remaining dough. Wrap the rolls and refrigerate until firm (for faster chilling, pop the wrapped rolls in the freezer).

3. Heat the oven to 375°F. Line 1 large cookie sheet with nonstick liner.

4. Arrange the rolls, seam side down, on a cutting board and cut into 1½-inch slices. Arrange on the prepared cookie sheet about 1 inch apart. Brush the tops with a little water and sprinkle with the chopped walnuts. Bake until deep golden brown, 23 to 25 minutes. Set on a rack to cool completely. (You can expect some of the jam to leak out.) Serve immediately or cover and store at room temperature.