1) If you’re using active dry yeast, dissolve it with a pinch of sugar in 2 tablespoons of the lukewarm water. Let the yeast and water sit at room temperature for 15 minutes, until the mixture has bubbled and expanded. If you’re using instant yeast, you can skip this step.
2) Combine the dissolved yeast (or instant yeast) with the remainder of the ingredients. Mix and knead everything together—by hand, mixer or bread machine set on the dough cycle—till you've made a smooth dough. Adjust the dough's consistency with additional flour or water as needed; but remember, the more flour you add while you're kneading, the heavier and drier your final loaf will be. If you’re kneading in a stand mixer, it should take about 5 minutes at second speed, and the dough should almost clean the sides of the bowl, perhaps sticking a bit at the bottom. In a bread machine (or by hand), it should beco0me soft, smooth, and elastic.
3) Place the dough in a lightly greased bowl. Cover the bowl, and allow the dough to rise, at room temperature, for 1 to 2 hours, or until it's nearly doubled in bulk. Rising may take longer, especially if you’ve kneaded by hand. Give it enough time to become quite puffy.
4) While the dough is rising, make the filling by whisking together the sugar, cinnamon, and flour.
5) Gently deflate the dough, and transfer it to a lightly greased work surface. Gently stretch and pat it into a 6" x 20" rectangle.
6) Brush the dough with the egg/water mixture; you won’t use all of it, but save what’s left. Sprinkle the dough evenly with the filling, leaving one short end bare.
7) Starting with the short (6") end covered with filling, roll the dough into a log. Pinch the ends to seal, and pinch the long seam closed.
8) Transfer the log, seam-side down, to a lightly greased 8 ½" x 4 ½" loaf pan. Tent the pan loosely with lightly greased plastic wrap.
9) Allow the bread to rise till it's crested about 1" over the rim of the pan, about 1 hour. Again, it may rise more slowly for you; let it rise till it’s 1" over the rim of the pan, even if that takes longer than an hour. While the dough is rising, preheat the oven to 350°F.
10) Brush the top of the bread very lightly with some of the reserved egg/water mixture, and sprinkle with additional cinnamon-sugar. Bake the bread for about 40 minutes, tenting it lightly with aluminum foil after the first 20 minutes. The bread’s crust will be golden brown, and the interior of the finished loaf should measure 190°F on an instant-read thermometer.
11) Remove the bread from the oven, and gently loosen the edges with a heatproof spatula or table knife. Turn it out of the pan onto a rack. Allow the bread to cool completely before slicing.