Combine the warmed milk, instant yeast and sugar in the bowl of a stand mixer fitted with a dough hook*. Add the flour, sourdough discard, beaten egg and salt. With the mixer on low, slowly pour in 2 Tablespoons of melted butter. Increase speed to medium and mix until a rough dough forms, about 2 minutes.
Transfer the dough to a smooth work surface and knead until smooth, about 3-4 minutes. The dough should be smooth, soft and not sticky. If needed, add more flour or milk (1 Tablespoon at a time) to reach your desired consistency.
Transfer the dough to a large oiled bowl and cover with plastic wrap. Let rise for 90 minutes, or until doubled in size.
Brush a 9x13-inch baking pan with 1 Tablespoon melted butter and set aside.**
Turn the dough onto a smooth work surface and divide into 15 equal-sized pieces. This doesn't have to be exact, but if you do want perfectly identical rolls, weigh the dough on a kitchen scale and divide that number by 15. For me, each roll weighs about 67 grams. Roll each piece of dough into a ball in the palm of your hand, then place the rolls into the prepared baking dish. Repeat until you have 15 rolls.
Cover the baking dish with plastic wrap and let the rolls rise for 60 minutes, until puffed and doubled in size.
Preheat the oven to 375℉. Brush the rolls with 2 Tablespoons melted butter, then sprinkle with flaky sea salt. Bake for 25-28 minutes until golden brown. If desired, brush with additional melted butter before serving.
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Notes
*This recipe can be made without a stand mixer. To do so, mix the dough in a large bowl with a wooden spoon, then knead by hand. **If doubling or tripling this recipe, I recommend splitting the rolls into multiple 9x13-inch baking pans and following the directions as written. To make this recipe with active sourdough starter, omit the yeast and replace the sourdough discard with active starter (200g). You will also need to increase the rise times. Note: This recipe was updated in October 2024 for a 9x13-inch baking pan.