Peel potatoes and cut into two. Place in a tray with garlic, rosemary, some olive oil, salt and black. Pepper. Bake in oven at 170C until ready. Allow the potatoes to cool and mash with a fork. Leave aside.
Activate the Lievito Madre three times at 12 o'clock. In proportions 50g of madre: 50g of white flour: 25g of water.
Mix the flour and 240g of water until a coarse dough is obtained and let it rest for 2h (autolysis) Cover with foil. Then, dissolve the Madrer with 20g of water and add to the dough and knead until smooth dough by hand or with a blender.
Put in a bowl and cover. After 40 minutes add the salt and knead 2-3 minutes. After 40 minutes, stretch and fold the dough on each side. Leave for 2 hours at room temperature 24-25C until the volume is doubled. Then cover well with foil and leave in the refrigerator for slow rising 12-14h. On the next day, leave the dough on a worktop to relax. Make a ball, cover with a cloth and let 30min rest. Form an batard or round loaf of bread, placing the potatoes evenly in the middle and letting it rise in banetone for about 4-6 hours until doubling the volume. Bake in a pan with a cover of 240-250C around 20min and then without cover for about 25-30min.