In a large mixing bowl, combine the warm milk and sugar. Sprinkle the active dry yeast over the mixture and let it sit for about 5 minutes until it becomes frothy.

Add the sourdough discard, melted butter, egg, vanilla extract, baking powder, salt, and half of the flour to the bowl. Stir until combined, then gradually add the remaining flour until a soft dough forms.

Turn the dough out onto a floured surface and knead for about 5 minutes until it becomes smooth and elastic.

Place the dough into a greased bowl, cover it with a kitchen towel, and let it rise in a warm, draft-free area for about 30 minutes, or until it doubles in size.

Once risen, roll the dough out into a rectangle about 1/4-inch thick. Spread the softened butter over the dough and sprinkle with brown sugar and cinnamon.

Starting from one end, tightly roll the dough into a log. Cut the log into 1-inch thick slices.

Place the rolls in a greased baking dish, cover, and allow them to rise for another 20 minutes.

Preheat your oven to 350°F (175°C), then bake the rolls for about 25 minutes or until golden brown.

While the rolls are baking, whisk together powdered sugar, milk, and vanilla extract to make a glaze.

Once the rolls are done, drizzle the glaze over the warm rolls and serve immediately. Enjoy!