Warm the beer in the microwave for 15 seconds. Pour it into a large bowl. Add the sourdough starter and brown sugar. Stir. Pour the packet of yeast over the top and let it sit for five minutes.
After five minutes, stir in the yeast. Next, add 2 cups of flour and stir until the dough forms a wet, shaggy ball. Set aside to autolyse for 20 minutes.
Next, add the salt and remaining ½ cup of flour. Mix just until the dough seems dry, not all of the flour will be incorporated yet.
Turn the dough out onto a clean surface. Use the flour in the bowl to dust your hands and work surface. Knead the dough until it forms a smooth ball-- it should take about five minutes. The dough will become increasingly sticky over the first 2-3 minutes. Use the flour in the bowl to dust your hands as needed.
Once the dough is smooth and only slightly tacky, place it into a well oiled bowl and let it sit at room temperature for at least an hour, or until doubled in size.
Preheat your oven to 425F.
Once the dough has doubled, turn it out of the bowl and divide it into six pieces. Roll the sections into long rods and then shape them as desired: rods, nuggets, etc. There's a great tutorial on how to shape pretzels here. After you’ve shaped the pretzels, bring a large pot of water to a boil. Slowly sprinkle in the baking soda-- if you add the baking soda too fast it will bubble over so add it slowly.
Boil the pretzels once at a time for 45 seconds on each side and then remove them to a parchment lined baking sheet (or two baking sheets if one isn’t big enough to hold all the pretzels).
Brush the boiled pretzels with an egg wash (a beaten egg + a splash of water) and sprinkle them with sesame seeds and flake salt.
Bake the pretzels at 425F for 20-22 minutes or until they are a deep amber brown color.