Begin by combining the lukewarm water with the active dry yeast and 1 tablespoon of brown sugar in a small bowl. Stir gently and allow it to sit for about 5 to 10 minutes, until it becomes frothy.
In a large mixing bowl, whisk together the remaining brown sugar, olive oil, and 4 of the 5 eggs. Add the foamy yeast mixture to this bowl.
In another bowl, mix the whole wheat pastry flour, all-purpose flour, and kosher salt. Gradually add this dry mixture to the wet ingredients, stirring until the dough begins to come together.
Transfer the dough to a floured surface and knead for about 8-10 minutes until it’s smooth and elastic. If the dough is too sticky, sprinkle a little more flour as needed.
Place the kneaded dough into a greased bowl, cover it with a clean kitchen towel, and let it rise in a warm place for about 1 to 2 hours, or until it has doubled in size.
Once the dough has risen, punch it down to release the air. Divide it into three equal portions for braiding. Roll each portion into long strands, about 12-14 inches long.
Carefully braid the strands together, pinching the ends to seal. Place the braided dough onto a greased baking sheet or in a loaf pan.
Cover the braid with a kitchen towel and let it rise again for about 30-45 minutes until it puffs up.
Preheat your oven to 350°F (175°C). Beat the reserved egg and brush it over the braided dough for a shiny finish.
Bake the challah in the preheated oven for 30-35 minutes, or until the bread is golden brown and sounds hollow when tapped on the bottom.
Remove the bread from the oven and let it cool on a wire rack. Slice and enjoy your Simple Whole Wheat Challah Bread fresh or toasted!