Activate the yeast by combining warm milk, yeast, and 1 tsp sugar in a small bowl. Let sit 5 to 10 minutes until foamy.
Mix the dough by whisking flour, remaining sugar, and salt in a large bowl. Add yeast mixture, softened butter, and egg. Mix until a shaggy dough forms.
Knead on a lightly floured surface for 8 to 10 minutes until smooth and slightly tacky. Or use a stand mixer with dough hook for 6 minutes.
First rise: Place dough in a greased bowl, cover, and let rise in a warm spot for 1 to 1.5 hours until doubled.
Make the filling by combining 1/2 cup sugar and cinnamon in a small bowl.
Shape the loaf: Punch down dough and roll into a 9x14 inch rectangle. Brush with melted butter, sprinkle filling, leaving a 1/2-inch border along one long edge.
Roll and place: Roll dough tightly from the long edge into a log. Pinch seam and place seam-side down in a greased 9x5 loaf pan.
Second rise: Cover and let rise 45 minutes to 1 hour until dough crowns about 1 inch above the pan rim.
Bake at 350°F (175°C) for 30 to 35 minutes. Tent with foil after 20 minutes if browning too fast. Internal temp should reach 190°F to 195°F.
Cool in pan for 10 minutes, then transfer to a wire rack. Slice only once fully cooled.