In a large mixing bowl, combine flour, sugar, salt, and instant yeast. Create a well in the center and add sourdough discard, melted butter, warm milk, and egg. Mix until a shaggy dough forms.

Turn the dough out onto a lightly floured surface and knead for about 5-7 minutes until smooth and elastic.

Place the dough in a greased bowl, cover with a damp cloth, and let it rise in a warm place for about 1 hour, until doubled in size.

Roll the dough out into a rectangle (about 12×18 inches). Brush the surface with melted butter, and sprinkle cinnamon and brown sugar evenly.

Starting from one long edge, tightly roll the dough into a log. Slice into 12 equal pieces.

Place the rolls in a greased baking dish, cover, and let them rise for another 30-45 minutes.

Preheat your oven to 350°F (175°C). Bake the cinnamon rolls for 20-25 minutes or until golden brown.

Drizzle with a simple icing made of powdered sugar and milk for that irresistible finish, if desired.