Beginning the day before you want to have sourdough hamburger buns, in the morning or afternoon:

Mix the flour, sourdough starter, water, salt, honey, and avocado oil together in a mixing bowl or in the bowl of your stand mixer. Stir to combine the ingredients.

Knead dough for 10 minutes. You can either do this by hand or in a stand mixer. The dough will be a little sticky. Next, cover with the bowl with plastic wrap and allow to ferment 6-12 hours, or at least until doubled.

After dough has risen and fermented for 6-12 hours, place dough in refrigerator overnight.

In the morning or afternoon of the next day, take the dough out of the refrigerator and turn out onto a clean surface.

Divide the dough into 8 equal pieces with a bench scraper, then roll each individual piece of dough on the counter to form a tight, smooth, round ball. Flatten the ball of dough slightly, until about ½-1 inch thick, and place onto a baking sheet lined with parchment paper.

Cover the rolls with a lightly damp tea-towel, and allow to rise until doubled (approx. 1-4 hours, depending on the temperature of your kitchen). Preheat your oven to 375 degrees.

Make your egg wash by cracking the egg into a small bowl and whisking vigorously with a fork for 1-2 minutes.

Brush your rolls with egg wash, then place in the preheated oven and bake for 18-20 minutes, until nicely browned on top.