Melt butter, honey, and salt on low in a saucepan. When it's melted and combined, turn off the heat, add your milk, and stir to combine. With a thermometer or your finger, test the temperature of the mixture. By thermometer, it should be no more than 105°F. By your finger...you should be able to comfortably hold it in for 10 seconds. If it's not this warm, turn the heat back on to warm it. If I use a heavy bottom pot, there is enough residual heat to heat the milk, if I use something like a thin enamel pot, there isn't.
Add the warm liquid to your mixer (or bowl you plan to mix the dough in) and add your pre-ferment.
Stir to combine; it's not going to combine super well until you start adding flour.
Add your flour, starting on the low end, and mix the dough, adding more flour as needed just until it's combined, but not a cohesive, nice dough.
Let sit 15-30 minutes to hydrate, then knead the dough.
Knead it by hand or with a machine until the dough starts to tear - this means it's had enough and needs to rest. If the dough sticks to the bowl or your hands, add a little more flour, but try not to add too much. It's not a stiff dough, it's on the softer side. Try wetting your hands/counter for kneading if it's sticking and you've already added a lot more flour.
Let it rise until doubled, about 6-8 hours.
Divide dough into 12-16 buns, depending on how big you like them. First I flatten into a rectangle, then I roll into a log. I set them all to rest on the tray and after a few minutes I flatten them out, as I dont want really tall hot dog buns.
Let rise until well risen, almost doubled! Don't rush this, it's a good few hours! This is a trick to getting good buns. If you started the dough in the morning, you should be able to bake right before dinner.
A way to tell if it's risen well is if you flour a finger and poke the dough, if the indent stays, the dough has given all it has to give. If it springs back (it wont be fast, a few seconds) it still needs to rise more.
For an optional gourmet look, beat an egg with a tablespoon of water. Brush the tops of the buns and sprinkle with sesame or poppy seeds for pretty buns.
Bake at 375°F for 15-20 min, until golden or internal temp is 180°F. Sourdough buns always take longer than regular yeast so when you're first getting to know sourdough baking, I highly recommend using an instant read thermometer to know that it's baked through.