Using a stand mixer fitted with the dough hook, combine the all-purpose flour, bread flour, yeast, 1/3 c sugar, salt, water, and 5 of the eggs. Beat on low speed for 3 to 4 minutes, or until all the ingredients are combined. Stop the mixer, as needed, to scrape the sides and bottom of the bowl to make sure all the flour is incorporated into the wet ingredients. Once the dough has come together, beat on low speed for another 3 to 4 minutes. The dough will be very stiff and seem quite dry.

With the mixer on low speed, add the butter, 1 piece at a time, mixing after each addition until it disappears into the dough. Continue mixing on low speed for about 10 minutes, stopping the mixer occasionally to scrape the sides and bottom of the bowl. It is important for all the butter to be thoroughly mixed into the dough. If necessary, stop the mixer occasionally and break up the dough with your hands to help mix in the butter.

Once the butter is completely incorporated, turn up the speed to medium and beat until the dough becomes sticky, soft, and somewhat shiny, another 15 minutes. It will take some time to come together. It will look shaggy and questionable at the start and then eventually it will turn smooth and silky. Turn the speed to medium-high and beat for about 1 minute. You should hear the dough make a slap-slap-slap sound as it hits the sides of the bowl. Test the dough by pulling at it; it should stretch a bit and have a little give. If it seems wet and loose and more like a batter than a dough, add a few tablespoons of flour and mix until it comes together. If it breaks off into pieces when you pull at it, continue to mix on medium speed for another 2 to 3 minutes, or until it develops more strength and stretches when you grab it. It is ready when you can gather it all together and pick it up in 1 piece.

Put the dough in a large bowl or plastic container and cover it with plastic wrap, pressing the wrap directly onto the surface of the dough. Let the dough proof (first rise) in the refrigerator for at least 6 hours or up to overnight. At this point you can freeze the dough in an airtight container for up to 1 week. 

Mix the 2/3 c sugar and ground cinnamon together in a small bowl. Line the bottoms of two 9x5 inch loaf pans with parchment paper, then spray the parchment and the sides of the pan with nonstick spray. Remove the dough from the fridge, and divide the cold dough in half, and roll out each into a 9-inch square. Generously sprinkle half of the the cinnamon sugar mixture all over the dough. Slowly and tightly, roll up the dough into a log. Place the log, seam side down, into one of the prepared loaf pans. Repeat the same with the second half of dough.

Cover with plastic wrap and let rise at room temperature for 3-4 hours or until the loaves have nearly doubled in size and reached the rim of the loaf pan. Preheat the oven to 350 degrees F, and brush the top of each loaf with the remaining beaten egg, using a small pastry brush. Sprinkle the thinly sliced almonds on top, then sprinkle with a bit more sugar. Bake for 40 minutes or until the tops and sides are very golden brown. Allow the bread to cool in the pans for about 20 minutes, then remove the loaves from the pans and let them finish cooling completely on cooling racks.

Store in an airtight bag or container for up to 4 days. Please do yourself a favor and toast a slice of this - pure heaven.