Make the starter: In the bowl of a stand mixer fitted with a dough hook, combine the flour, yeast, salt, and 2⁄3 cup water. Mix on low speed until a smooth dough forms, about 2 minutes. Scrape into a large bowl, cover with plastic wrap, and let stand at room temperature for four 4 hours.
Make the bread: In the bowl of a stand mixer fitted with a dough hook, combine 2 1⁄2 oz. (about 1⁄4 cup) of the starter with the beaujolais, yeast, and salt. Stir until smooth. Add flour and mix on low speed until the dough forms. Increase speed to medium and knead until smooth, about 5 minutes. Add chorizo and knead for 5 minutes more. Transfer to a lightly greased bowl, cover with plastic wrap, and let stand until dough is doubled in size, about 1 hour.
Uncover the dough, divide into 2 balls (about 1 1⁄2 lbs. each), and shape each into an 11-inch-long, 3-inch-wide log with tapered ends, placing the seam side facing up. Transfer each to a parchment paper-lined baking sheet, cover with plastic wrap and let stand until dough springs back lightly when touched, about 1 1⁄2 hours.
Position a rack in the middle of the oven and another rack on the bottom, and heat the oven to 400°. Place a small metal pan on the lower rack and pour in 1 cup boiling water; then place the bread loaves on the upper rack and bake until crust is golden brown, about 35 minutes. Transfer loaves to a rack and let cool to room temperature before serving.