Combine sourdough starter, water, flour in a bowl. Mix until dough is shaggy. This is where you may need to add a little more water. Use standing mixer or your clean hands. Cover dough & let rest 30 mins.
Add salt, sugar, grated butter, yeast to the bowl and knead for 3 to 6 minutes. Dough should be silky and elastic. Really work that butter into the dough.
Cover and leave dough to rise. One hour. Dough needs to double in size.
Butter or grease your loaf pan.
Tip dough out onto a clean counter, sticky side up. Ease dough out and fold over on all four sides. Shape into a log/rectangle. Place inside loaf pan, seam side down.
Let the rise in the pan for one hour. Cover with a damp cloth.
Bake on 350° for 40 to 45 minutes or until golden brown. Preheating the oven is okay.
Butter grates easier when it's super cold or frozen.
More notes in the blog post on www.johnsonhomenc.com