In a mixing bowl, dissolve the yeast into the 1/3 cup warm water and mix in the teaspoon sugar. Let the mixture sit for 10 minutes, or until it thickens. Meanwhile, in a separate medium bowl combine the 2/3 cup sugar, salt, bread flour and corn meal. Set aside.
When the yeast is thick, add the oil, 2 eggs and warm water and mix well with a whisk. Add the dry ingredients and mix well with the dough hook of a stand mixer or with a wooden spoon. Sprinkle 1 tbsp. flour on your counter and place the dough on top. Knead until you have a mostly smooth dough, adding another tablespoon of flour if necessary.
Grease the bowl with the remaining 1 tsp. oil and return the dough to the bowl and rub your oiled hand on top of the dough. Cover with a dish towel and let rise for 1 hour.
Divide the dough in half and shape each piece into a three-braided challah. Place loaves on a parchment- or Silpat-covered baking sheet and let rise for 45 minutes.
Preheat the oven to 350°F.
Place the remaining egg into a small bowl and add a little less than 1 tsp. water and beat well. Brush on top of the loaves and sprinkle the pumpkin seeds on top. Bake for 30 to 35 minutes, or until golden.