Mix the two flours form into a mound and make a well in the center. Crumble the yeast into the well and sprinkle with the sugar. Pour in the milk and water and add the salt. Knead the dough until it is smooth and supple.
Sprinkle the dough with flour, cover and place in the oven set to 50°C (approximately 125°F) for 45 minutes. The dough should clearly show cracks on the surface and should have doubled in volume. Keep the oven door open a crack with a wooden spoon handle.
Mix the cornstarch with 250 ml (approximately 1 cup) water, bring to a boil and allow to cool until the liquid is lukewarm. Meanwhile, knead the dough on a floured surface vigorously until it is smooth and elastic. Shape into a round loaf and place on a greased baking sheet.
Cover the dough and let sit at room temperature for 30 minutes. Preheat the oven to 250°C (approximately 475°F). Place a bowl with boiling water in the back of the oven. Brush with the cornstarch mixture and score the dough with a sharp knife several times diagonally.
Bake in the preheated oven for 10 minutes, then turn down the oven to 200°C (approximately 400°F) and bake for another 50 minutes. Heat the remaining starch solution again and brush the freshly baked bread with it. Cool on a wire rack, slice and serve.