In a clean jar or small bowl, combine the starter, flour, and water. Mix until no dry flour remains. Cover loosely and let rest at room temperature (70-75°F / 21-24°C) overnight.

The levain is ready when it has doubled in size, is domed on top, and looks bubbly throughout. A small spoonful should float in water (float-test). If your kitchen is cool, this may take up to 12 hours.

In the bowl of a stand mixer (or a large mixing bowl), combine the bread flour, warm milk, and levain. Mix on low with the dough hook for 2 minutes until a shaggy dough forms. Let rest 20 minutes. This short rest gives the flour time to hydrate before we add the fat.

Add the egg, sugar, and salt. Mix on low for 2 minutes until incorporated, then increase to medium and knead for 5 minutes. The dough should start pulling away from the sides of the bowl.

With the mixer on medium-low, add the softened butter one tablespoon at a time. Wait until each piece is mostly absorbed before adding the next. Once all the butter is in, increase to medium and knead for 6-8 minutes until the dough is smooth, elastic, and pulls cleanly from the bowl. It should be soft and slightly tacky but not sticky. By hand: knead on a lightly floured surface for 12-15 minutes total after adding butter.

Shape the dough into a ball and place in a lightly greased bowl. Cover with plastic wrap or a damp towel. Perform 3 sets of stretch-and-fold at 45-minute intervals during the first 2 hours. After the folds, leave the dough undisturbed.

Let the dough ferment at room temperature (75-78°F / 24-26°C) until it has risen 60-80% and looks puffy and airy. This typically takes 4-5 hours total (including fold time), but trust the dough, not the clock. In a cool kitchen, it may take 6 hours. Do not wait for doubling. You need this dough rollable, not blown out.

Once bulk fermentation is complete, cover the bowl tightly and refrigerate for 30-45 minutes. You want the dough firm enough to roll thin without sticking, but not so cold that it fights you. The butter in this dough firms up quickly in the fridge, which is exactly what makes shaping easier.

Heat olive oil in a large skillet over medium heat. Add garlic and cook 30 seconds until fragrant. Add spinach in batches, tossing until fully wilted. Season lightly with kosher salt and black pepper.

Transfer to a colander and press out every bit of moisture. This step matters. Wet filling ruins the layers. Let cool to room temperature, then roughly chop.

In a bowl, combine the drained spinach, feta, mozzarella, cream cheese, and red pepper flakes. Mix until it holds together as a spreadable paste. Taste and adjust seasoning.

Turn the dough onto a lightly floured surface. Divide into 4 equal pieces (roughly 150-160g each). Shape each into a ball, cover with a towel, and rest for 10 minutes.

On a lightly floured surface, roll each piece into a 12-inch circle. They don't need to be perfect, but keep them close to the same size.

Place the first circle on a parchment-lined baking sheet or round pizza pan. Divide the filling into 3 equal portions. Spread one portion over the first circle, leaving a 1-inch border. Stack the second circle on top. Spread another portion. Repeat with the third circle and remaining filling. Place the fourth circle on top with no filling.

Place a small bowl or glass (about 3 inches wide) in the center of the dough stack and press lightly to mark a circle. Do not cut through. This is your guide for the cuts.

Using a sharp knife or bench scraper, cut the dough outside the center circle into 16 equal strips. Cut from the edge of the center circle to the outer edge. The easiest way: cut into quarters first, then each quarter in half (8 strips), then each strip in half again (16 strips).

Take two adjacent strips and twist them away from each other (outward) twice, then pinch the ends together to form a point. Repeat around the entire circle until you have 8 points.

Carefully remove the guide bowl. You should have a sunflower-star shape with a clear center and 8 twisted points.

Cover loosely with plastic wrap and let proof for 30-45 minutes until slightly puffed. Because sourdough moves slower than instant yeast, you may need up to 60 minutes. The dough should look relaxed and pillowy, not dramatically risen.

Preheat your oven to 375°F (190°C) with a rack in the center position.

Whisk the egg and milk together for the egg wash. Brush gently over the entire surface of the star, getting into the twists.

Scatter black sesame seeds over the center circle only. This creates a dramatic contrast against the golden egg-washed dough.

Bake for 25-30 minutes until deep golden brown. The layers should be set and the filling visible between the twists. If the top is browning too fast, tent loosely with foil after 20 minutes.

Let cool on the pan for 15 minutes before serving. Pull-apart style, right from the center. The cheese should still be warm and stretchy.

Cut dough into 4 equal pieces (~150-160g each). Shape into balls, rest 10 minutes covered.

Roll each piece into a 12-inch circle on a lightly floured surface.

Layer: dough, filling, dough, filling, dough, filling, dough (no filling on top). Leave 1-inch border on each filling layer.

Press a 3-inch bowl or glass into the center to mark (don't cut through).

Cut from center circle to outer edge: quarters first, then halves of each quarter, then halves again.

Take 2 adjacent strips, twist outward twice, pinch ends together. Repeat for 8 points.

Preheat oven to 375°F (190°C) with a rack in the center position.

Brush entire surface with egg wash (1 egg + 1 tbsp milk). Get into the twists.

Scatter black sesame seeds over the center circle only.

Bake 25-30 minutes until deep golden brown. Filling should be bubbling between the twists. Tent with foil if browning too fast after 20 minutes.

Let cool on the pan for 15 minutes. Serve pull-apart style.