Prep your produce: halve the Roma Tomato, stem the Serrano Chile (leave seeds for more heat or remove for milder salsa), quarter the White Onion, and peel the Garlic Clove.
Warm a dry cast-iron skillet or heavy pan over medium-high heat and add a small drizzle of Neutral Oil to just coat the surface.
Place the halved Roma Tomato, whole Serrano Chile, quartered White Onion, and Garlic Clove in the hot pan and cook, turning occasionally, until the skins are charred and blistered and the onion has softened — about 8–12 minutes.
Transfer the charred vegetables to a blender or food processor. Add a handful of chopped Cilantro, a pinch (or to taste) of Salt, and a splash of Water to help the blender along.
Pulse or blend to your preferred texture — a few short pulses for a chunky salsa or longer for a smoother sauce. Check seasoning and add more Salt or Water to adjust consistency.
Optional: For a deeper, cooked flavor, pour the blended salsa back into the skillet and simmer gently for 3–5 minutes, stirring occasionally. Taste and correct seasoning one last time.
Let the salsa cool slightly, then serve at room temperature with chips, tacos, grilled proteins, or store in the refrigerator for up to 4–5 days.
