½ cup sourdough discard (unfed, straight from the fridge)
½ cup whole milk, warmed to 110°F (43°C)
1 teaspoon active dry yeast
4 tablespoons unsalted butter, melted
¼ cup unsalted butter, softened (for filling)
½ cup brown sugar, packed (for filling)
2 tablespoons ground cinnamon (for filling)
1 cup powdered sugar (for icing)
2–4 tablespoons whole milk or heavy cream (for icing)
½ teaspoon vanilla extract (for icing)
Instructions
Preheat oven to 375°F (190°C). Grease a 9×9 inch baking dish with butter or line with parchment paper.
In a large bowl, whisk together warm milk and active dry yeast. Let sit for 5-10 minutes until foamy.
Add sourdough discard, melted butter, granulated sugar, and flour to the bowl. Mix until a shaggy dough forms.
Turn dough out onto a lightly floured surface and knead for 2-3 minutes until smooth.
Roll dough out into a 9×12 inch rectangle.
Mix together softened butter, brown sugar, and cinnamon for filling. Spread evenly over dough, leaving a ½-inch border on one long side.
Tightly roll dough up from long side opposite the border. Pinch seam to seal.
Use a sharp knife or dental floss to cut log into 9 equal pieces.
Place cinnamon rolls cut-side up in prepared baking dish.
Bake for 20-25 minutes until golden brown and cooked through.
While rolls bake, whisk together powdered sugar, milk (or cream), and vanilla extract until smooth.
Let rolls cool for 5 minutes, then drizzle icing on top. Serve warm.
Notes
Sourdough discard does not need to be active or fed. Use it straight from refrigerator, any age or consistency works.
Milk should be warm to touch (110°F), not hot, to activate yeast without killing it.
For extra flavor, add a pinch of salt to dough or splash of vanilla extract to filling.
Roll dough tightly to prevent filling from spilling out during baking.
Make ahead: prepare through Step 9, cover tightly, refrigerate overnight. Let sit 15 minutes at room temperature before baking, add 3-5 minutes to baking time.