Add yeast, sugar and water to a large bowl. Let yeast bloom for a few minutes, and then add salt and 2 cups of flour. Mix to combine.
Add in ¼ cup of flour at a time, and knead until the dough comes together and cleans the bottom of the bowl. You may need to use less or more flour as bread making depends on the temperature of your kitchen.
Place dough into a greased bowl. Cover with plastic wrap and place in warm environment until doubled, about 1 hour.
Turn dough onto lightly flour dusted bench. Using a rolling pin, roll dough into a 16x12 inch rectangle. Cut in half, vertically, creating two 8x12 inch rectangles.
Roll each half of the dough up tightly, beginning at the 12 inch side. Place onto a parchment lined baking sheet.
Make diagonal slashes in the loaves, then cover, and let rise until doubled, approximately 30 minutes.
Preheat oven to 375°F (190°C). Mix egg yolk with water and brush onto loaves. Bake for 20-25 minutes, or until golden brown. Baguettes are best consumed the day they are baked.