Combine the warmed milk, instant yeast, and sugar in the bowl of a stand mixer*. Add the flour, sourdough discard, beaten egg, garlic powder and salt. With the mixer on low speed, slowly add 2 Tablespoons of melted butter. Increase speed to medium and mix until a shaggy dough forms.
Transfer the dough to a smooth work surface and knead until a smooth dough forms, about 3-4 minutes. The dough should be smooth and slightly tacky (but 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 greased bowl and cover with plastic wrap. Let rise for about 90 minutes, or until doubled in size.
Brush an 8x8-inch baking pan** with 1 Tablespoon melted butter and set aside.
Turn the dough onto a smooth work surface and divide into 9 equal-sized pieces. This doesn't have to be exact, but if you want perfectly identical rolls, weigh the dough and divide that number by 9 to determine how much the dough for each roll should weigh. Roll each piece of dough into a ball in the palm of your hand, then place the rolls into the prepared baking pan. Repeat until you have 9 rolls.
Cover the baking pan with plastic wrap and let the rolls rise for 60 minutes, until puffed and doubled in size. They should be touching in the pan.
Preheat the oven to 375℉. Brush the rolls with 1 Tablespoon melted butter. Bake for 20-25 minutes until golden brown.
While the rolls bake, melt the remaining 3 Tablespoons unsalted butter. Remove from heat, then add the garlic powder and chopped parsley and stir to combine. Remove the rolls from the oven and immediately brush with the parsley and butter mixture. Sprinkle with flaky sea salt and serve while warm.
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Notes
*You do not need a stand mixer to make this recipe. You can make the dough in a large mixing bowl with a wooden spoon, then knead by hand. **If you are doubling or tripling this recipe, use 2 (for doubling) or 3 (for tripling) 8x8-inch baking pans, then continue with the directions as written for each pan.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.