Place the flour in a medium bowl and pour the milk and water over top. Whisk until combined. It may be lumpy at this point, but it will smooth out.
Microwave at 30 second intervals, whisking in between, until it reaches 145-150°F or the mixture is that of a thick, smooth paste; let cool to lukewarm.
Make the dough
Add the ingredients into the bowl of a stand mixer in the order in which they are listed (wet first, then dry). Knead on low until the dough comes together, and then increase the speed to medium and knead for 5 minutes.
Scrape dough into the center of the bowl, cover, and let rise until doubled in size. This could take anywhere from 2 hours up to 8 hours, depending on the time of year or ambient temperature of your proofing area. Go by the looks versus the time (if it's been 6 hours and still doesn't look any different, let it go longer). Sourdough always takes longer to proof than commercial yeast.
Once the dough has fully proofed, refrigerate it overnight.
Shape and proof
Remove the dough from the fridge and knead it on a well-floured surface. It is a rather soft and sticky dough, so just do your best and add more flour as necessary. It doesn't need to be perfect. You're just trying to remove a lot of the air bubbles and make the dough smoother.
Divide dough into roughly 80 gram pieces and roll each portion into a tight ball, using extra flour as necessary.
Place rolls in a well-greased baking dish and cover with plastic wrap. Set baking dish in a warm, draft-free area to proof until rolls are nearly doubled in size. The time it takes to proof will vary, depending on the ambient temperature in your proofing area. Focus more on what the rolls look like than the time.
Bake
Preheat oven to 350°F. When rolls are fully proofed, brush them with melted butter and bake for 20 minutes, or until they bounce back when pressed lightly. They will be ever so lightly golden brown on top so don't overbake them in an attempt to achieve a darker golden brown color.
Immediately upon removing from the oven, brush them again with any leftover melted butter. Let cool slightly before indulging in the softest gluten free roll you'll ever have!
Notes
Rolls will keep, well covered, at room temperature for up to 5 days and should STILL be soft. For longer storage, I recommend freezing them individually on a baking sheet and then storing in an airtight storage container or ziploc bag. They will last in the freezer for up to 3 months.