Thaw the puff pastry sheet, according to package directions. Spread an even layer of sugar onto a pastry board. Place the thawed pastry sheet on top of the sugar. Sprinkle a layer of sugar on top of the pastry sheet. Gently roll the pastry sheet, pressing with a medium firmness to push the sugar into the dough. Spread a very thin layer of seedless raspberry jam onto the puff pastry, leaving about a 2" border all the way around.Turn the dough with the short side facing you. Fold the end closest to you about 1 1/2" inward. Do the same from the other side. With a rolling pin, press the dough together. Be careful not to press too hard, or the jam will ooze out. Again, fold another 1 1/2" inward on each side. Now, fold one side on top of the other, add additional sugar and press again with a rolling pin. Using a sharp knife, cut about 3/8" slices and place about 1 1/2" apart on parchment paper. Freeze for 15 minutes, or refrigerate for 30 minutes.Don't skip this step! Preheat the oven to 375˚F. Bake for 15 to 20 minutes, depending on your oven, until golden brown. Place on a cooling sheet. These are excellent warm, or cold with a cup of hot coffee or hot tea. NOTE: You can freeze these and bake at a later time.