In a large bowl or stand-mixer add yeast, sugar, table salt and bread flour and warm water. Let stand five minutes until small bubbles appear. Using the dough hook attachment, add all-purpose and spent grain flours and mix on low until the dough comes together. Increase speed to medium and mix for about 5 minutes until dough is elastic and smooth.
Form dough into a ball and place in oiled mixing bowl, turning once to coat. Let rise 30 minutes covered in a warm, damp dish towel. Next, lay the dough out on a floured surface and knead for 1 minute.
Divide dough into 8 balls and place on an oiled baking sheet or cupcake tin, score top of each roll, cover with a damp dish towel and let rise again for about 20 minutes.
Preheat oven to 425⁰F. Bring water and beer to a boil in a large pot on the stove top. When rolls have risen, add the baking soda to the boil (it will foam up a bit). Using a slotted spoon, boil rolls for 2 minutes per side. Transfer rolls to baking sheet with rolls scored side up. Sprinkle with sea salt and bake 12 minutes; let stand to cool before serving.