For starter, preheat oven to 200°C. Line a baking tray with baking paper. Place kumara on tray and roast until golden and very tender (1½ hours). Cool completely, then peel skin. Set aside 100gm (½ cup) flesh, cover and refrigerate. Transfer 200gm (1 cup) remaining flesh to a bowl and mash with a potato masher until smooth. Add 100gm of each flour and 200ml water and stir to combine. Cover and set aside to ferment at room temperature (2 days). Discard half the starter, then stir through another 100gm of each flour and 200ml water. Leave to ferment at room temperature (1 day). Repeat for another 3 days until starter is bubbling and ready to use.

Combine 300gm starter with flour, yeast, spices, honey and 380ml water in a bowl and mix until it forms a slightly wet dough. Coarsely crush reserved roasted kumara, add to dough and mix with your hands. Set dough aside to rest (30 minutes). Add 1 tbsp fine salt and mix through dough until completely dissolved. Leave dough to prove until rested and risen by one-third (30 minutes).

Knock back dough, then fold dough over itself from four sides. Set aside to rest (30 minutes), then repeat process three times. Cover and refrigerate dough overnight. Bring dough to room temperature 1½ hours before cooking.

Preheat a woodfire or charcoal barbecue to medium. Dust a surface with extra flour. Divide dough into 8 small balls (about 160gm each). Working with one ball at a time, flatten and gently stretch by hand until 7.5mm thick. Grill flatbread, turning and brushing occasionally with lamb fat, until lightly charred and cooked through (5-7 minutes). Serve warm, drizzled with fat and seasoned with salt flakes.