Step-by-Step
In a large bowl, dissolve the yeast in the warm water.
Stir in 1 tablespoon of the sugar and about 2 cups / 240g (8.5 oz) of the flour.
Mix until you have a soft, spongy dough, also known as a sponge.
Cover the bowl with a towel and set it in a warm, draft-free place to rise for about 45 minutes, until it's puffed up and bubbly.
Add the milk, the remaining 1 tablespoon (15 ml / 0.5 fl oz) of sugar, the salt, and the melted butter to the sponge and stir well to combine. Gradually work in the remaining flour, about a cup at a time, until a fairly stiff dough forms that pulls away from the sides of the bowl.
Turn the dough out onto a well-floured surface.
Knead for 10 to 15 minutes, adding small amounts of flour as needed to prevent sticking, until the dough is smooth and elastic. You should be able to stretch a small piece into a thin 'windowpane' without it tearing.
Form the dough into a ball and place it in a large, buttered bowl, turning it over once to coat the entire surface with butter.
Cover the bowl with a light towel and let it rise in a warm place for 45 minutes to 1 hour, or until the dough has doubled in size.
Gently punch down the dough to release the air.
Divide it in half and shape each half into an oblong loaf or a large braid.
Place the loaves on buttered baking sheets, cover them loosely with a towel, and let them rise again in a warm place for about 30 minutes, or until they have nearly doubled.
Preheat your oven to 425°F / 220°C.
In a small bowl, beat together the egg yolk and the tablespoon of milk to create the glaze. Gently brush this mixture over the tops of the loaves.
Place the loaves in the preheated oven.
Bake for 5 minutes, then lower the oven temperature to 375°F / 190°C.
Continue baking for another 35 to 40 minutes, or until the loaves are a deep golden brown and sound hollow when tapped on the bottom.
Transfer the hot loaves to wire racks to cool completely before slicing. This prevents the interior from becoming gummy.