Remove the husks from the tomatillos and rinse them thoroughly under running water to eliminate their sticky coating. Finely chop the white onion, mince the garlic, and prepare the serrano pepper. If a milder salsa is desired, remove the seeds from the pepper before mincing.

In a large saucepan, combine the tomatillos, onion, serrano pepper, and garlic. Stir in the cilantro, oregano, salt, and cumin, ensuring the ingredients are well distributed. Pour in 2 cups of water and bring the mixture to a boil over high heat. Once boiling, reduce the heat to medium-low and allow it to simmer for 10 to 15 minutes, or until the tomatillos soften and turn a deeper green.

Carefully transfer the cooked mixture into a blender in batches. If a thinner salsa is preferred, include some of the cooking water. Blend until smooth for a silky texture, or pulse a few times for a chunkier consistency.

Taste the salsa and adjust seasoning as needed. If additional heat is preferred, blend in an extra serrano pepper. If a more citrusy flavor is desired, a small amount of lime juice may be added.

Once the salsa reaches the desired consistency and flavor, transfer it to a serving bowl and allow it to cool slightly. Serve with tortilla chips, or use as a topping for tacos, burritos, or enchiladas.