Heat buttermilk and butter in a small saucepan set over low heat until butter is melted. Let sit for a few minutes to cool, or until temperature is between 120-130°F.
Add 2 ½ cups of the flour, salt, sugar, yeast, garlic, and herbs to the bowl of a stand mixer fitted with a dough hook (or a large bowl if you plan to mix and knead by hand).
Add the buttermilk mixture and mix until it forms a wet dough. Add remaining flour 1/4 cup at a time until the dough clears the sides and no longer sticks to your fingers.
Continue kneading with dough hook or by hand until dough is smooth and elastic, about 7-8 minutes with a stand mixer.
Form dough into a ball and place in a greased bowl. Cover with plastic wrap and let rise until doubled, about 1 hour.
Gently punch down dough and knead a few times to bring it back into a ball.
Roll dough out into a rough 9x15 inch rectangle. Starting at one of the 9-inch ends, roll dough into a log. Place in a greased 9x5 inch loaf pan, cover with plastic wrap, and let rise again until doubled, 45-60 minutes.
Meanwhile, preheat oven to 375°F. Brush loaf with egg wash and bake bread until top is deep golden brown and loaf sounds hollow when tapped, 30-35 minutes. Remove bread from pan immediately and let cool on a wire rack.
Bread is best the day it is baked, but you can wrap it and store at room temperature for up to 3 days.