Preheat the oven to 400°F. Line a baking sheet with parchment paper.
Lightly flour your work surface then unfold one sheet of puff pastry. Using a rolling pin, roll it into a 9x12-inch rectangle.
Using a sharp knife or pizza wheel, cut the rectangle into a large triangle. Cut a 3x2-inch rectangle from the scraps to form the tree trunk.
Place the triangular piece of puff pastry on the baking sheet and place the tree trunk at the bottom of the triangle.
In a small bowl, stir together the jam and rosemary. Spread it into an even layer across the tree and trunk.
Lightly flour your work surface and unfold the second sheet of puff pastry. Roll it into a 9x12-inch rectangle and cut out the same triangle and rectangle shapes.
Place the second triangle atop the first triangle covered with the jam. Place the second rectangle atop the first rectangle covered with the jam. Gently press the two layers together.
In a small bowl, whisk the egg with 1 tablespoon water. Brush the eggwash atop the puff pastry.
Using a sharp knife or pizza wheel, start 3 inches from the top of the triangle and make 1-inch cuts down the sides while leaving a 1-inch section down the middle. Twist the strips.
Bake the puff pastry until it is golden brown and puffed, 12 to 15 minutes. Remove it from the oven, dust it with confectioners' sugar and serve.
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