Place 3 1/2 cups flour, water, salt, and yeast in a large glass or ceramic bowl; mix by hand until just incorporated. Cover the bowl with plastic wrap and place it on a thick kitchen towel on the counter. Let sit on the counter for 12 to 18 hours.

Sprinkle a clean work surface with 2 tablespoons flour. Scrape the dough (it will be sticky) from the bowl onto the work surface. Stretch and fold the dough over several times, working in some of the flour. Shape into a round loaf.

Place parchment paper inside a slow cooker, making sure to drape it up the sides. Place the dough in the center of the slow cooker, and trim off any parchment paper that hangs over the rim. Place a double layer of paper towels over the slow cooker and secure the lid.

Cook on High without peeking for 2 hours. Remove bread to a cooling rack and allow to cool completely before slicing.