Try to keep the metal buñuelos mold in the hot oil as much as you can in between preparing the buñuelos. Ideally the night before using the metal mold for the first time, cure the mold to ensure it is nonstick: Bring 2 cups of water up to a boil in a saucepan. Immerse the mold part into the water. Remove the saucepan from the heat and let cool for 2 to 3 hours. Dry off the mold completely. Immerse the mold part into 1 cup of oil that is very hot in a saucepan. Remove the saucepan from the heat and let the mold sit overnight in the oil. Once the mold is cured, you do not need to cure it again — only on its first use. Do not wash the mold; using water or a towel to wipe is sufficient, and do not use anything abrasive.