In a large bowl, sprinkle the yeast over the warm water and stir until dissolved. Add the sourdough starter, whole wheat flour, 2 ½ cups bread flour (312g) and salt. Mix with a wooden spoon until the dough is stiff and elastic, about 2 minutes.

Flour your kneading surface. Turn the dough out onto the surface and knead for 8-10 minutes until the dough no longer sticks to your hands. Add spoonfuls of flour while kneading if dough seems too sticky.

Grease a large bowl with olive oil and add the kneaded dough. Turn once or twice to coat the dough with olive oil. Cover with a clean kitchen towel and allow to rise for 30 minutes.

Punch down the dough and reshape into a smooth ball. Return to the greased bowl and cover with the towel. Allow to rise for 30-45 minutes.

For the last time, punch down the dough and reshape into a smooth ball. Line a baking sheet with parchment paper and sprinkle lightly with cornmeal. Place the dough on the parchment paper and cover with the kitchen towel. Allow to rise for 45-60 minutes until doubled in size.

During the last 15 minutes of rise time, adjust the wire racks in your oven to accommodate the bread and a steam pan underneath. Heat your oven to 475°F (246°C) degrees.

Using a pastry brush, brush the prepared bread with water and dust with a sprinkling of flour. Using a very sharp knife or a razor blade, make two vertical slashes on the top of the dough and two horizontal slashes to form a square pattern on top of the bread. Place the empty broiler pan on the bottom rack of the oven for 5 minutes to heat.

Place the ice cubes in a measuring cup. You will need a sturdy pan such as the bottom tray of an enameled broiler rack for making steam.

Place the prepared bread on the middle rack in your oven. Carefully pull out the broiler pan and add the ice cubes. Step back slightly to protect yourself from the cloud of hot steam. Push the pan of ice into the oven under the prepared bread and gently close the oven door. Do not open the oven for at least 10 minutes. Bake for 30-45 minutes. The bread will be ready when the crust is firm and sounds hollow when tapped with your fingernail.