In a stand mixer, combine the sourdough discard and warm water, stirring until well combined. Gradually add the bread flour, mixing until you achieve a shaggy dough. Let the mixture rest for 30 minutes.

Add salt, sugar, softened butter, and instant yeast to the dough. Mix on low speed until combined, then increase to medium speed, kneading for 3-6 minutes.

Transfer the kneaded dough to a greased bowl and cover with a damp cloth. Let it rise in a warm area until doubled in size, about 1 hour.

Gently turn the dough onto a floured surface, shape into a rectangle, and roll tightly into a log. Place in a greased loaf pan, seam side down.

Cover the loaf pan with a towel and let the dough rise again until it peeks above the rim of the pan, about 1 hour.

Preheat your oven to 180°C (350°F). Bake for 40-45 minutes until golden brown and sounds hollow when tapped.

Remove from the oven and turn out onto a wire rack. Allow it to cool completely before slicing.