In a large mixing bowl or stand mixer, combine flour, sugar, yeast, and salt. Mix well to combine all dry ingredients.

In a separate bowl, whisk together warm milk, melted butter, egg, and vanilla extract until well combined.

Pour the wet ingredients into the dry ingredients and mix on low speed until a shaggy dough forms. Increase speed to medium and knead for 6-8 minutes until dough is smooth and elastic.

Place dough in a greased bowl, cover with a clean kitchen towel, and let rise in a warm place for 60-90 minutes until doubled in size.

While dough rises, prepare the cinnamon filling by mixing together sugar, cinnamon, and softened butter until well combined and spreadable.

Grease a 9x5 inch loaf pan and set aside. Punch down the risen dough and turn it out onto a lightly floured surface.

Roll the dough into a large rectangle approximately 9x18 inches. Spread the cinnamon filling evenly across the surface, leaving a 1/2-inch border around the edges.

Starting from the short end, tightly roll the dough into a log shape. Pinch the seam and ends to seal, then place seam-side down in the prepared loaf pan.

Cover the pan with a towel and let rise for 30-45 minutes until the dough has risen about 1 inch above the rim of the pan.

Preheat oven to 350°F (175°C). Bake the bread for 40-45 minutes until golden brown on top and internal temperature reaches 190°F. If the top browns too quickly, tent with foil.

Remove bread from oven and let cool in pan for 10 minutes, then transfer to a wire rack to cool for another 10-15 minutes.

While bread cools, prepare the icing by whisking together powdered sugar, milk, vanilla, and salt until smooth and pourable. Add more milk if needed for desired consistency.

Drizzle the vanilla icing generously over the warm bread, allowing it to run down the sides. Let the icing set for a few minutes before slicing and serving.