Combine starter, water, honey, and flour in a stand mixer bowl (or large bowl for hand mixing). Mix with dough hook on low (speed 1–2) for 30 seconds until shaggy—no dry flour. Cover and autolyse 30 minutes.
Add salt and plant butter. Mix on medium (speed 2–3) 1 minute to incorporate, rest 30 minutes.
Knead 3 minutes until elastic; rest 10–30 minutes if warm. Knead another 2–3 minutes until smooth, glossy, and pulling from bowl sides (windowpane test: thin sheet without tearing). Wholemeal makes it slightly bumpy from bran.
Cover and bulk ferment at room temp (21–24°C / 70–75°F) 4–6 hours until ~1.5–1.8x volume, puffy with bubbles. Warmer kitchen = faster; cooler = slower.
Grease tin with plant butter. Turn dough onto unfloured surface (sticky side up). Gently pat to rectangle (short side facing you), pop bubbles, roll tightly into log, tuck ends under for tension.
Place seam-side down in tin. Cover and proof 2–4 hours at room temp until domed 1 cm above rim—poke test: slow spring back.
Preheat oven to 180°C (350°F) fan / 200°C (390°F) conventional. Bake 35–45 minutes until golden, internal temp 93–96°C (200°F), or hollow tap on bottom. Brush top with melted plant butter post-bake for softness.
Cool in tin 10 minutes, then on rack 2+ hours before slicing. Stores in plastic bag 4–5 days or freezes well.
