Make Dough: In a large mixing bowl, whisk together 2 cups flour, 1 tsp salt, 1 Tablespoon white sugar, and yeast. Add water and stir until no dry spots remain. The dough will be very stick, but just scrape down the sides and you stir.
First Rise (30 minutes): Cover the dough with a clean dish towel and leave it on the counter to rise until puffy, 30 minutes.
While dough is rising, brush a loaf pan with cooking oil or spray with nonstick cooking spray. Place the loaf pan on a sheet pan (this will just catch any cinnamon crunch pieces that fall off during baking).
Make Cinnamon Streusel: In a small mixing bowl, whisk together brown sugar, ¼ cup white sugar, cinnamon, and ¼ tsp salt. Add melted butter and stir until evenly combined. Add 1 ¼ cups flour and mix with a fork until the mixture is even (it will be thick and dry).
Assemble Bread: After dough has been rising for 30 minutes, use your hands to scatter about ¾ of the cinnamon streusel mixture over top, breaking it apart with your hands as you go. Gently fold the cinnamon mixture into the dough until it is evenly combined.
Tip the dough into the prepared loaf pan, using a spatula if needed to help ease it out. Brush the surface of the loaf with whisked egg and then crumble the remaining cinnamon streusel over top.
Preheat oven to 375°F / 190°C.
Second Rise (30 minutes): Place the bread near the oven and leave to rise until it nears the top of the loaf pan, about 30 minutes.
Bake bread until the top is golden brown and crisp, 40 to 45 minutes. (The bread is done with it reaches 190°F / 88°C in the center.)
Allow the bread to cool for 10 minutes in the loaf pan. Gently turn it out onto a rack to cool completely. (Make sure to allow it to completely cool before slicing it - if it's still warm it may compress and that can give the center a gummy texture.)
Slice and serve.