Focaccia tramezzino con lievito madre
all-purpose flour (about 1 kg) • milk, at room temperature (500 ml) • water, at room temperature (500 ml) • granulated sugar (20 grams) • sourdough starter (about 300 grams) • sunflower oil (about 140 grams) • fine salt (30 grams) • egg yolk • milk for brushing (50 grams) • Sesame seeds, • Poppy seeds, • arugula (160 grams) •