This is how the guacamole at Monte Albán might have tasted. For historical fidelity, we have omitted the garlic and citrus juice because these ingredients were introduced by the Spanish. Fortunately, the tartness of the Tomatillo Purée makes up for the lack of lemon juice. Spread on the Shrimp-and-Guacamole Tostadas, or serve as a dip with baked tortilla chips.
Combine Tomatillo Purée, serrano chile, salt, and avocados in a bowl, and mash the mixture to desired consistency. Cover and chill.