1.Add 400 grams flour and 100 grams milk to a microwave safe bowl and whisk them together. Microwave for 30 seconds, then stir and microwave for another 30 seconds. The mixture should now be a thick slurry, but if it’s not, microwave it in 10 second intervals until it has thickened.
2.Add 90 grams milk, sugar, yeast, 1 egg, 240 grams flour, 1 1/4 teaspoon salt, 56 grams butter, and flour/milk mixture to the bowl of a stand mixer fitted with the dough hook attachment. Knead the mixture on medium speed for about 15-20 minutes. The dough is ready when it is no longer sticking to the sides or the bottom of the bowl, and passes the windowpane test.
3.Once the dough is done kneading, shape it into a ball and place it back into the mixing bowl. Cover the mixing bowl with plastic wrap and place it in a warm area to rise until doubled in size about 1 hour and 30 minutes.
4.Meanwhile, in a small mixing bowl, melt 42 grams of butter. Mix the butter together with the brown sugar and cinnamon to form a paste. Set aside. Spray a 9"x5" loaf pan with cooking spray and line it with parchment paper. In a small dish beat 1 egg with 1 tablespoon milk and then place in the fridge for the egg wash.
5.Once the dough has doubled in size, punch it down to remove excess air. Transfer the dough to a clean and lightly floured surface, then roll it out to a 12″x16″ rectangle. If the dough keeps springing back a lot while rolling it out, let it rest for 5 minutes before continuing.
6.Spread the butter, cinnamon and sugar mixture over the dough. Using a pizza cutter, cut the dough in half once through the longer side, then slice each piece into 8 pieces, so you have 16 strips. Roll up the mini cinnamon rolls.
7.Layer the cinnamon rolls into the loaf pan. Start out with placing some rolls standing up facing the sides of the pan, then place some face up in the middle of the pan. After that, randomly but evenly distribute the rest of the rolls in the pan. Lightly cover the pan with a towel, and let the loaf rise in a warm environment until doubled in size about 45 minutes.
8.Preheat the oven to 350°. Brush the egg wash over the rolls. Place the loaf pan on top of a sheet pan. Bake the loaf for 35-40 minutes. Use a thermometer to check when the rolls are done cooking (200°F).
9.In a small mixing bowl, whisk together the powdered sugar, 2 tablespoons milk, vanilla and 1/8 teaspoon salt until smooth. Allow the cinnamon roll loaf to sit in the pan for at least 20 minutes before transferring it out. Pour the glaze over the warm loaf, then slice, serve, and enjoy!