Combine the sourdough starter with the melted butter in a large bowl. Add the sugar, baking soda, salt, and 1 cup of flour. Mix until a dough starts to form.
Add more flour, as needed, to make a soft dough. Knead the dough a few times to bring it together. However, don’t over-knead. The goal is to bring the bread together, without making a strong gluten structure.
Roll the dough out on a floured surface until it is 1/2 inch (1 cm) thick. Using a biscuit cutter, cut out as many circles as you can. The scraps of dough can be quickly kneaded together and hand-formed into 1 or 2 more circles.
Lay the circles out on a greased baking sheet. This is a quick bread, so they don’t need to rise.
Beat together the egg, water, and salt to make an egg wash. Brush the tops of the rolls with the egg wash. You can also sprinkle on some seeds or other toppings. See notes for options.
Bake for 20 min, until the buns are cooked through and browning.