Add 1/2 cup flour to a shallow dish. Combine remaining flour, beer, salt, pepper, and garlic in a medium bowl, stirring well.
Heat olive oil in a large skillet. Dredge fish in flour, then dip in beer batter. Place fish in hot oil. Cook 4-5 minutes per side or until browned and crispy. Drain on paper towels.
Buns
Add warm water to the bowl of a stand mixer. Add 1 egg, butter pieces, and honey. Add flour, buttermilk powder, and gluten. Add salt to the side of the bowl. Make a well in the center of the dry ingredients and add the yeast to the well. Fit mixer with a dough hook and mix on speed 1 or 2 for 5 minutes or until a dough ball forms and cleans the sides of the bowl. Dough ball should be tacky but not sticky, and should spring back when lightly touched with a finger. If dough is too sticky, add flour, one tablespoon at a time. If dough is too dry, add water, 1 teaspoon at a time.
Cover dough ball with a clean towel and let rise 1 hour. Turn mixer to speed 1 for 10 seconds. Pour dough onto a clean work surface and divide into 8 equal portions. Roll each portion into a ball and place on a parchment lined baking sheet. Flatten slightly with the palm of a hand. Cover with a clean towel and let stand another 30 minutes. Meanwhile, preheat oven to 375.
Separate remaining egg and discard the white. Place yolk in a small bowl. Add 1 Tablespoon of water to the yolk, and beat with a fork until frothy. Brush tops of buns with the egg glaze and sprinkle with sesame seeds, if using. Bake at 375 for 15-22 minutes. Allow to cool before slicing. Save 4 buns for a future use. (They freeze well.)
Coleslaw
Add coleslaw mix to a large bowl. Add remaining ingredients to a blender and blend until smooth. Combine dressing and coleslaw mix until well mixed.
Sandwiches
Add 1 filet to the bottom half of a bun. Top with coleslaw and pickles. Top with bun top. Repeat with remaining filets and buns. Serve any remaining coleslaw on the side.
Notes
We used Trader Joe's Organic Mayonnaise for testing purposes. Spectrum also makes a clean version of mayonnaise.