In the morning (or night before): In a small glass jar, dissolve your 25g of starter culture and 15g of sugar into 35g of water. Whisk together until smooth, then stir in 75g of bread flour.

Knead briefly inside the jar into a firm, tight ball. Cover loosely and let it ferment at room temperature 74–78°F (23–26°C) for 6 to 8 hours until it triples in volume, softens up, and fills the jar with an airy, sweet aroma.

In your stand mixer bowl, combine the 115g of cold milk, 50g of heavy cream, 1 large egg, 40g of sugar, and all 140g of your mature sweet stiff starter broken up into a few pieces. Whisk briefly to combine, then dump all 275g of bread flour right over the liquids.

Attach your dough hook. Mix on low speed for 3 to 4 minutes until a rough, shaggy mass forms with no dry flour remaining. Let the dough rest undisturbed in the bowl for 15 minutes.

Add the 5g of fine sea salt. Turn your mixer up to medium-high speed and knead continuously for 7 to 8 minutes until the gluten network tightens up and pulls cleanly away from the sides of the bowl.

Drop in the 25g of soft room-temperature butter. Keep running on medium-high speed for another 5 to 7 minutes until the fat incorporates perfectly and the dough becomes incredibly smooth, glossy, and elastic.

Cover the bowl and let bulk ferment for 2 hours at a warm 78–82°F (25–28°C) until it looks slightly puffy and light.

The Three-Cylinder Shape: Tip the dough out onto a clean workspace. Using a bench scraper and kitchen scale, divide the dough mass cleanly into 3 equal pieces. Round each piece into a smooth ball, cover loosely with plastic wrap, and let them rest on the counter for 30 minutes to relax the gluten.

Take one rested ball and flatten it into an oval with a rolling pin. Fold the left third inward over the center, then fold the right third over that like a letter. Use your rolling pin to flatten this folded strip lengthwise into a long rectangle, then roll it up tightly from the short bottom edge into a dense cylinder. Repeat for the other 2 pieces.

Line your loaf pan with parchment paper. Arrange the 3 shaped cylinders side-by-side inside the pan. Cover loosely and let them proof at room temperature for 3 to 4 hours until the highest curves of the dough rise to exactly 1 cm below the top rim of the pan.

Preheat your oven to 350°F (175°C).

Slide the pan onto the middle rack and bake for 30 minutes until the top turns a gorgeous, uniform golden brown.

Remove from the oven and carefully lift the hot loaf out of the pan using the parchment paper edges. Let cool completely on a wire rack before tearing or slicing into its cloud-like interior.