Mix the starter dough together and let it ferment overnight or at least 4 hours.
Add the main dough ingredients except the fat and knead until elastic and gluten formed.
Add the fat and knead until it passes the window pane test. (not more than 10 minutes)
Rest and proof until the dough doubles.
Punch down (important to get fine crumbs) and shape dough.
Proof till the dough doubles its size again.
Bake on the lowest shelf in a convection oven at 180C for 30 minutes.