Step 1: In a large bowl, whisk together warm milk, 1/2 cup granulated sugar, and yeast. Let sit for 5-10 minutes until foamy, indicating the yeast is active.
Step 2: Add 1/2 cup melted butter, egg, and salt to the yeast mixture. Stir to combine.
Step 3: Gradually add the flour, 1 cup at a time, mixing with a wooden spoon or a stand mixer with a dough hook until a shaggy dough forms. Turn the dough out onto a lightly floured surface.
Step 4: Knead the dough for 5-7 minutes until it's smooth and elastic. Alternatively, use a stand mixer with a dough hook on medium-low speed for 5 minutes.
Step 5: Place the dough in a lightly oiled bowl, turning once to coat. Cover with plastic wrap and let rise in a warm place for 1-1.5 hours, or until doubled in size.
Step 6: While the dough rises, prepare the cinnamon filling: In a small bowl, combine 1 cup granulated sugar and ground cinnamon. Melt 1/4 cup butter in a separate bowl.
Step 7: Once the dough has doubled, gently punch it down. Roll the dough out on a lightly floured surface into a rectangle approximately 12x18 inches. Cut the rectangle lengthwise into three equal strips.
Step 8: Brush each strip generously with melted butter, then sprinkle liberally with the cinnamon-sugar mixture.
Step 9: Stack the three buttered and sugared strips on top of each other. Cut the stacked dough into 6-8 equal squares. Place these squares upright in a greased 9x5-inch loaf pan, alternating the direction of the layers for a pull-apart effect.
Step 10: Cover the loaf pan loosely with plastic wrap and let rise again for 30-45 minutes, or until puffed up.
Step 11: Preheat your oven to 375°F (190°C).
Step 12: Bake for 25-30 minutes, or until the top is golden brown and a wooden skewer inserted into the center comes out clean. If the top browns too quickly, tent loosely with foil.
Step 13: While the bread bakes, prepare the glaze: Whisk together powdered sugar, 2 tablespoons milk/cream, and vanilla extract until smooth. Add more milk/cream if needed to reach desired drizzling consistency.
Step 14: Once baked, remove the bread from the oven and let it cool in the pan for 5-10 minutes before transferring to a wire rack. Drizzle generously with the prepared glaze while still warm. Serve immediately and enjoy!