You (probably) have no idea how difficult it is to find a recipe online for real sourdough pretzels. I looked through quite a few, but most of them called for commercial yeast. How is that sourdough? I did find two that were made with a base of sourdough starter. The one I ended up using came from the rec.food.sourdough recipe FAQ.
I made a few changes based on the various pretzel recipes I read before finding this one (so what I'm posting here is not the exact recipe from the mailing-list, but it's what I used). It looks like boiling the pretzels first (bagel style!) makes them brown more evenly and have a nicer texture. I also noticed from the steam rising from the back burner that the wet pretzels also put a lot of water vapor in the air, most likely accounting for their fantastic crust. Plus it gives the salt something to stick to without going to the trouble of an egg & cream wash, though that would probably also give the pretzels a nice brown colour and a bit of a sheen.
(I may try it that way next time. The original recipe called for the pretzels to rise 30 minutes after shaping, then to be brushed with 2 tablespoons milk or heavy cream stirred together with one egg yolk, then salted and baked without the boiling.)
I altered the rising instructions from those given, partially because of my schedule, and partially because I wanted a stronger sour flavour from the dough. I had removed my white flour starter, Scully, from the fridge three days earlier and fed her a bit every twelve hours, since I wasn't sure when I'd be baking, and wanted the yeast to be at a peak as often as possible. Once I had made the dough, I let it rise in the fridge for five hours, then at room temperature for another four before rolling it out. The flavour was excellent, with a faint, but distinct sourdough taste. They go very well with mustard. (And thanks to that picture, I can now identify the paint on our dining room walls as "honey mustard yellow", but I think it's called something else entirely.)
Sourdough pretzel recipe
Yield: 20 pretzels, about 4 to 5 inches across, hard crust, soft center.
1-1/2 cups proofed batter
1 cup hot water
2 tablespoons butter
3 tablespoons sugar
2 teaspoons salt
5-1/2 cups all purpose flour
1. Let all ingredients and utensils come to room temperature.
2. Add the 2 tablespoons butter, the 3 tablespoons, sugar, and the 2 tsp salt to the cup of hot water. Cool to lukewarm.
3. Put the proofed batter into a warm bowl. Add the cooled water mixture.
4. Add 4 cups of flour, 1/2 cup at a time, stirring after each addition.
5. Turn out onto a floured board and knead in approximately 1-1/2 cups more of the flour. The dough will be very stiff. (gk: They ain't kiddin'!)
6. Place the dough in a greased bowl, turn over, and cover. Let set for 2 hours to proof.
7. On a board which has been scraped clean of flour break of pieces of the dough about the size of a large egg. Roll each piece out with the palm of your hands until it is about 18 inches long and about 1/2 inch in diameter. Twist into the shape of a pretzel.
8. Bring a pot of water to a rapid boil. Drop as many pretzels as will fit without touching into the water and cook about 30 seconds after they have risen to the top. (Or longer, if you like a chewier pretzel.)
9. Remove to a baking sheet and sprinkle with coarse salt.
10. Bake in a preheated 425*F oven for 15 minutes, until golden brown. Remove and cool on wire racks.