1. Put the flour, yeast, sugar, and salt in a bowl. With 4 fingers, mix the dough until the flour is fully incorporated.
2. Add the oil and knead the dough for 5 minutes until smooth. Then form a ball.
3. Cover it with a damp cloth or plastic wrap and let it rest in a turned-off oven for 40 minutes to 1 hour. (The dough should double in size).
4. Slice onions, carrots, and bamboo. Heat oil in a pan and sauté the onion with minced garlic and chopped ginger.
5. Add the ground meat, carrots, bamboo, and bean sprouts and sauté everything.
6. Add sake, soy sauce, and water.
7. Simmer for 3 minutes and add the potato flour mixture (make a mixture by combining potato flour with 3 tablespoons of cold water) and mix well over low heat for 2 minutes.
8. Reserve in the refrigerator.
9. Divide the dough into 8 pieces and form balls, then flatten the dough into discs. (about 5 to 8 mm thick and thicker in the middle)
10. Place a disc of dough in your hand and place 2 teaspoons of filling in the center.
11. Make the first fold by pinching the rightmost part of the dough between your index finger and thumb.
12. Fold the upper part of the dough with your left index finger to form a second fold on top of the first one, and pinch the dough.
13. Continue to make the other folds. Always close each fold over the previous one.
14. It is important that the filling remains securely sealed inside the dough and that the cooking juices do not leak out.
15. Cut 10 squares of parchment paper the size of the nikuman balls.
16. Place them on the paper and steam for 10 minutes in a steamer basket.
17. Serve immediately.
18. (It is possible to reheat them for a few minutes in a steamer basket or in the microwave).