Combine the warm water, instant yeast, sugar, flour, sourdough discard and salt in the bowl of a stand mixer or large mixing bowl. With the mixer on low, slowly add 2 Tablespoons melted butter. Increase speed to medium and mix until a shaggy dough forms.
Transfer the dough to a smooth work surface and knead until smooth, about 2-3 minutes. The dough should be smooth and slightly tacky (but not sticky). If needed, add more flour or water (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.
Prepare two baking sheets lined with parchment paper; set aside.
Turn the dough onto a smooth work surface and divide into 10 equal-sized pieces. This doesn't have to be exact, but if you do want perfectly identical breadsticks, weigh the dough with a kitchen scale and divide that number by 10 to determine how much the dough for each breadstick should weigh. Roll each piece of dough into a rope about 10 inches long, then place on the prepared baking sheets with space between each breadstick.
Cover the baking sheets with plastic wrap and let the dough rise for 60 minutes, until puffed and doubled in size.
Preheat the oven to 375℉. Brush the breadsticks with 1 Tablespoon melted butter. Bake for 18-20 minutes until puffy and just slightly golden.
While the breadsticks are baking, melt the remaining 3 Tablespoons unsalted butter. Remove from heat, then add the dried parsley, garlic powder, and salt, and stir to combine. Remove the breadsticks from the oven and immediately brush with the herb and butter mixture. Serve while warm.
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Notes
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.