In a large bowl or bowl of a stand mixer, whisk together the sourdough discard, warm milk, sugar, eggs, and melted butter.

Add the instant yeast and mix to combine.

Add the flour and salt.

Mix the ingredients with a dough hook attachment at low speed or by hand until a shaggy dough forms.

Knead the dough for 5–8 minutes at medium-low speed until the dough is smooth, elastic, and slightly tacky but not sticky.

Add 1–2 tbsp more flour or milk if needed to achieve a soft dough.

Cover the bowl with plastic wrap or a damp towel and let the dough rise at room temperature (the temperature of your kitchen will affect how fast or slow the dough rises) for 1-3 hours, or until it has doubled. 

On a lightly floured surface, roll the dough with a floured rolling pin into a large rectangle, approximately 12x18 inches. 

Spread the dough with softened butter evenly over the dough surface with a brush, rubber spatula of offset spatula, then mix the brown sugar and cinnamon together and sprinkle this mixture evenly over the buttered dough. 

Roll the dough up tightly from the long edge. Use baker's twine or unflavored dental floss , or a sharp knife to cut the roll into 9 even rolls (about 2" thick each).

Place the rolls in a greased 9×9 inch baking dish.

Cover the dish and let the rolls rise in a warm place for 1–2 hours, or until they become puffy. When gently pressed, the dough should spring back slowly. The exact rise time depends on your kitchen temperature. You can also place the rolls in the fridge overnight. 

Preheat the oven to 350°F.

Bake the cinnamon rolls for 25–30 minutes or until they turn golden brown. Tent the pan with foil in the last 5 minutes if the rolls seem to be browning too quickly.

While the rolls are cooling, in a small bowl, whisk all glaze ingredients until smooth and the mixture reaches your desired consistency. Spread the glaze over the warm cinnamon rolls for a melted effect, or wait until they cool for a thicker glaze.