Heat a heavy, medium pot over medium heat. Add the chorizo, breaking up the large pieces with a wooden spoon. Saute until almost crisp, about 6 minutes. Using a slotted spoon, transfer the chorizo to paper towels to drain.
Add the butter and onions and cook over medium-high heat until the onions are soft, about 5 minutes. Add the garlic and saute until fragrant, about 3 minutes longer. Add the tequila and clam juice and bring to a boil over medium-high heat, scraping up the browned bits at the bottom of the pan. Add the clams to the pot, cover and reduce the heat to medium. Cook until the clams open wide, 10 to 12 minutes (discard any clams that remain unopened). Return the chorizo to the pot and stir to combine. Divide between 2 bowls, sprinkle with the chopped cilantro and serve with the loaf of sourdough.