Place chicken, 1 liter water, half the onion, half the garlic and 4 g salt in a saucepan. Bring to a gentle simmer and cook 20–25 minutes, until the thickest part of each piece reaches 165°F. Move the chicken to a clean dish and retain the broth, onion and garlic.

Meanwhile, toast the pepitas in a dry skillet over medium-low heat for 4–6 minutes, stirring, until some puff and turn lightly golden. Transfer to a plate immediately. Reserve 10 g for the garnish.

In another saucepan, simmer the tomatillos in water to cover for 6–8 minutes, until softened and changed in color. Drain. Cool ingredients before blending if your blender does not permit hot liquids.

Blend the remaining toasted pepitas, tomatillos, serrano, cilantro except the reserved leaves, remaining raw onion and garlic, cooked onion and garlic from the broth, and 400 ml of the broth. Process until finely ground, stopping to scrape down as needed.

Heat the oil in a wide pot over medium-low heat. Add the sauce carefully and cook 8 minutes, stirring along the bottom. Add 300 ml more broth and simmer gently 12–15 minutes. Add remaining broth or water as needed until the sauce coats a spoon but still flows.

Return the chicken to the sauce and heat about 5 minutes, or until the chicken and sauce are 165°F throughout. Add up to the remaining 2 g salt as needed. Serve six portions with the reserved pepitas and cilantro.