Combine 60g starter, 60g bread flour, 30g whole milk, and 20g sugar. Mix until no dry flour remains — it'll feel stiff. Shape into a rough ball and place in a jar. Cover and ferment 4–6 hours at 75–78°F (24–26°C) until roughly doubled.

Combine flour, warm milk, eggs, sugar, and all levain. Mix on low until shaggy, then rest 20–30 minutes (fermentolyse). Knead 5–7 minutes until smooth. Add softened butter 1 tbsp at a time (8–12 min), then salt, vanilla, and zest. Check for windowpane.

Transfer to oiled bowl. Ferment 4–6 hours at 75–78°F. Perform 2–3 stretch-and-fold sets in the first 1.5 hours, spaced 30 min apart. Fold in raisins during second set if using. Dough should feel puffier and lighter — may not double. That's fine.

Turn onto lightly floured surface. Fold edges to center, flip seam-side down, rest 10–15 min. Shape into tight round and place in greased tall pan. Optional: reserve dough for decorative cross/braid on top.

Same-day: Cover, proof 3–5 hours at room temp until dough crowns above pan edge. Overnight (recommended): Cover tightly, refrigerate 8–12 hours. Remove 1–2 hours before baking.

Preheat to 350°F (175°C). Brush with egg wash. Bake 35–40 minutes. Tent with foil at 20 min if browning fast. Done at 190–195°F (88–90°C) internal. Cool in pan 10 min, then turn out. Don't slice until fully cooled (45–60 min).

Whisk 60g powdered sugar + 15g milk + drop of vanilla. Drizzle over completely cooled loaf.