In a large mixing bowl, combine the warm water and active sourdough starter. Stir gently until the starter is mostly dissolved.

Add the bread flour and mix with a dough scraper or your hand until no dry flour remains and a shaggy dough forms. Cover the bowl with plastic wrap or a damp tea towel and let it rest for 30 minutes (autolyse).

Sprinkle the salt over the dough. Incorporate the salt by dimpling it into the dough with wet fingers, then perform a set of stretch and folds. Lift a portion of the dough from one side, stretch it upwards, and fold it over itself. Rotate the bowl and repeat 3-4 times until the salt is fully integrated.

Cover the bowl and let the dough rest for 30 minutes. Over the next 2-3 hours, perform 3-4 more sets of stretch and folds every 30-45 minutes. The dough should become progressively smoother, more elastic, and develop strength. After the last set, the dough should be visibly airy and jiggly.

Cover the bowl and allow the dough to bulk ferment at room temperature (70-75°F / 21-24°C) for another 2-4 hours, or until it has increased in volume by about 30-50%. Alternatively, you can place the covered dough in the refrigerator overnight (8-12 hours) for a cold bulk ferment, which enhances flavor.

While the dough is in its final bulk ferment or after cold fermentation, prepare the filling. In a small bowl, combine the softened butter, minced garlic, chopped fresh parsley, chives, dried oregano, black pepper, and a pinch of salt. Mix well until everything is evenly combined.

Lightly flour your work surface. Gently turn the dough out onto the floured surface. Stretch or pat the dough into a rough rectangle, then use a rolling pin to roll it into a rectangle approximately 10x14 inches (25x35 cm) and about 1/4 inch (0.6 cm) thick.

Evenly spread the herb and garlic butter mixture over the entire surface of the dough rectangle, leaving a small 1/2-inch (1.2 cm) border along one of the long edges.

Starting from the long edge opposite the butter-free border, carefully roll the dough into a tight log. Pinch the seam closed along the unbuttered edge.

Using a sharp knife or bench scraper, slice the log lengthwise down the middle, creating two long halves. Ensure the ends remain slightly attached (about 1 inch) to help with twisting, or slice completely for a more open braid.

With the cut sides facing up, carefully twist the two halves around each other to form a spiral. Try to keep the cut sides exposed as much as possible for a beautiful marbled effect.

Carefully transfer the twisted dough into a lightly greased loaf pan. Gently tuck in any loose ends.

Cover the loaf pan with plastic wrap or a damp tea towel and let it proof at room temperature for 1-2 hours, or until visibly puffy and increased in size by about 25-50%. The dough should look aerated but not over-proofed. If using dough from cold fermentation, this proofing might take longer (2-3 hours).

Preheat your oven to 375°F (190°C) with a rack in the middle position during the last 30 minutes of proofing.

Optionally, brush the top of the loaf with a little olive oil for a crispier crust. Bake for 35-45 minutes, or until the crust is deeply golden brown and sounds hollow when tapped.

Remove the loaf from the oven and immediately turn it out onto a wire rack to cool completely before slicing. This prevents the bottom from getting soggy.