Step 1Bring 3 cups of water to a boil and pour it carefully over the sweet rice flour. Mix thoroughly with a wooden spoon. The mixture will be dry and crumbly, but keep stirring and it will come together to make a smooth dough.
Step 2In a small bowl, combine the sesame seeds, sugar, salt and the remaining 1 tablespoon of water. Set aside.
Step 3Separate the pine needles from the branches, taking care to remove all the brown ends. Wash thoroughly in cold water.
Step 4Lay wet cheesecloth or cloths to cover the bottom of a flat, shallow steamer. Layer pine needles on top of the wet cloth.
Step 5Knead the dough about 30 minutes. The longer you knead, the smoother and chewier the rice cake.
Step 6Tear off about 1 tablespoon of dough, knead it a few more times, then roll it around between your palms until you have a round ball about 2 inches in diameter. Press a dimple in the dough ball with one of your thumbs, and continue to turn and press the dough until you have a bowl shape.
Step 7Spoon about 1/2 teaspoon of the sesame seed filling into the rice bowl, compacting it, but not filling it completely. Gently squeeze together the edges of the bowl into a fat half-moon dumpling shape to seal. Lay it on the pine needles. Repeat until you run out of dough and/or filling.
Step 8Set the rice cakes in the steamer, making sure they aren't touching each other to prevent sticking when cooking. You'll need to do this in batches. Cover the rice cakes with another layer of pine needles and steam until the cakes become slightly translucent in color, about 10 minutes. Remove them from the pine needles at once so they don't stick.
Step 9Serve warm or at room temperature.