In a large mixing bowl, combine warm milk (not listed, assumed to be gently warmed to about 110°F), yeast, and a teaspoon of sugar. Let sit until foamy, about 5 minutes, indicating activation. Meanwhile, in a separate bowl, whisk together flour, remaining sugar, salt, and softened butter.
Add the sour cream and egg to the activated yeast mixture, stirring until combined. Pour this wet mixture into the dry ingredients and stir with a spatula until a shaggy dough forms. Transfer to a floured surface and knead gently for about 5 minutes until smooth and elastic.
Place the kneaded dough in a greased bowl, cover with a damp cloth, and let rise in a warm area until doubled in size, approximately 1 hour. The dough should look puffy and slightly spring back when touched.
Preheat the oven to 375°F (190°C). Punch down the risen dough and roll it out on a floured surface into a rectangle about 12x18 inches. Spread melted butter evenly over the surface, then sprinkle with cinnamon and granulated sugar to form the filling. Roll the dough tightly from the long side into a log, then cut into 8 equal pieces.
Arrange the cinnamon rolls in a greased baking dish, spacing them slightly apart. Bake in the preheated oven until golden brown around the edges, about 20-25 minutes. Remove from oven and let cool slightly before optionally drizzling with powdered sugar glaze.
Serve warm, optionally topped with a glaze made from powdered sugar and a small amount of milk or sour cream for added sweetness and richness. Enjoy the tangy, sweet, and tender cinnamon rolls.
