Sift the flour into a warm bowl and combine in the cornmeal and salt. Dissolve the fresh yeast in a cupful of the warm water and sprinkle with a spoonful of the flour. Work the yeasty liquid into the flour, adding as much of the water as you need to make a soft, sticky, rather wet dough. Work the dough to stretch the gluten (push and tug), form it into a ball, and dust with flour. Set it to rise under a damp cloth in a warm place for a pair of hours until more than doubled in bulk: you need well-risen dough with nice big foam to get a crisp light bread.
Dust your hands and the table with flour. Scoop out the dough and punch it down roughly with your fists to disperse the air. Cut the dough in half, work each piece into a ball, and dust generously with flour.
Move to a greased baking sheet, cover with a cloth, and let rise again in a warm kitchen for 30 minutes.
Preheat the oven to 400°F (200°C). Bake the bread for about an hour, until well-risen and hollow-sounding when you tap the bottom. Don't undercook the loaves, or they'll be heavy. Perfect with a spoonful of Queijo da Serra (mountain cheese: ripe and runny in winter and spring, firm and pungent later in the year) or a few slivers of the region's magnificent salt-cured hams and sausages.
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