Mix the starter, warm water, and pickle brine until mostly dissolved. Add both flours and stir until a shaggy dough forms with no dry spots. Sprinkle salt over the top, cover, and let rest for 40 minutes. If the dough feels dry, add water 1 tablespoon at a time.

Knead the dough for about 2 minutes to work in the salt, then stretch one side upward and fold it over itself. Cover and let rest for 30 minutes. The dough should feel soft and slightly elastic.

Add the chopped pickles and dill, then perform another stretch and fold to incorporate. Rest for 30 minutes. If pieces fall out, gently press them back in.

Repeat two more rounds of stretch and folds with 30-minute rests in between, until the dough becomes smoother and holds its shape better.

Let the dough rise, covered, until about 75% larger, around 4 hours at 74°F. It should look puffy with small bubbles. Transfer to a floured surface, rest 10–15 minutes, then shape and place seam-side up in a floured banneton. If it spreads too much, tighten it with a gentle fold.

Proof in the fridge overnight (up to 12 hours) or at room temperature for about 1½ hours. Preheat the oven with a Dutch oven inside to 450°F. Turn the dough onto parchment, score at least ½ inch deep, place into the hot pot, cover, and bake for 25 minutes. Uncover, reduce heat to 435°F, and bake another 20 minutes until deep golden and crisp. The crust should sound hollow when tapped.

Cool on a rack for at least 1 hour before slicing to prevent a gummy texture.