From Cooking in Marfa by Virginia Lebermann and Rocky Barnette
1/2 cup fresh lime juice
1/4 cup avocado oil
6 firm-ripe hass avocados, halved and pitted
kosher salt and freshly ground black pepper
1/2 medium red onion, cut into 1/8 inch dice
2 large jalapeños, seeded and cut into 1/8-inch dice
1/2 cup finely chopped cilantro
1/2 teaspoon ground cumin
2 tablespoon extra virgin olive oil
Preheat the grill (barbecue) or a cast-iron grill pan (griddle pan) to very high heat.
In a small bowl, combine the lime juice and avocado oil. Season the avocados with salt and pepper. Brush them liberally with the lime juice mixture.
Place the avocado halves flesh side down on the grill until they are slightly charred, about 4 minutes. Flip them and grill on the skin side for 1-2 minutes to heat the avocados through but not char the skin. Remove from the grill and brush the flesh side with more lime juice mixture. Set aside to cool to room temperature.
Squeeze the avocado flesh into a large molcajete or bowl. It should slip right out of the skins from the grilling. Add the onion, jalapeños, cilantro, cumin, olive oil and any remaining lime juice mixture from the grilling process.
Process with the mano in the molcajete or with a spool in the bowl to get a semi-smooth paste with some small chunks about the size of a pea. Season with salt and pepper.
Serve immediately. Guacamole can be stored in a pastry bag or airtight container for up to one day.