Make the Streusel: In a small bowl, whisk together the flour, brown sugar, and cinnamon for the topping. Cut in the cold, cubed butter with a pastry blender or your fingertips until it resembles coarse crumbs. Refrigerate until needed.

Activate Yeast: In a stand mixer bowl, combine warm milk, sugar, and yeast. Let sit for 5-10 minutes until foamy.

Mix Dough: To the yeast mixture, add the softened butter, egg, salt, and half the flour. Mix with the dough hook. Gradually add the remaining flour and knead on medium speed for 6-8 minutes until the dough is smooth and elastic.

First Rise: Form dough into a ball, place in a greased bowl, cover, and let rise in a warm place for 1-1.5 hours, or until doubled.

Prepare Filling: In a small bowl, mix together the brown sugar, cinnamon, and flour for the filling.

Assemble: Punch down the dough and roll it into a 10x14 inch rectangle. Sprinkle the filling evenly over the top. Roll it up tightly into a log and pinch the seam to seal.

Second Rise: Place the log in a greased 9x5 inch loaf pan. Cover and let rise for 45-60 minutes. Preheat oven to 350°F (175°C) during the last 15 minutes of rising.

Bake: Sprinkle the chilled streusel over the loaf. Bake for 40-50 minutes, or until golden brown and an internal thermometer reads 190°F (88°C). Tent with foil if it browns too quickly. Let cool before slicing.