Day 1: Melt 30g of the butter and set aside.
In a bowl, add the flour, sourdough starter, salt, water and melted butter. Start with 100ml of the water and mix it until it forms a ball. Add in the remaining 20 ml if necessary. Then place it in the refrigerator for 8-20 hours.Leave the remaining 200g of butter at room temperature ready for day 2. Day 2: Take the 200g of room temperature butter and slice it into 4 slices. Take two sheets baking paper and lay out the slices of butter on one of the sheets, into a square. Place the second sheet of baking paper overtop. Using a rolling pin, roll the butter out into a 20 x 15cm rectangle.
Place the butter rectangle in the refrigerator for around 10 minutes to firm up slightly, but ensure it’s still a little pliable and not rock hard.
Take the dough from the refrigerator and roll it out lengthwise in front of you into a 20 x 30cm rectangle.
Now, take the butter from the refrigerator and remove one sheet of baking paper. Lay the unwrapped side down on the bottom 2 thirds of the dough rectangle. Fold over the top third, over the butter, and press it down. Take the bottom third and fold that over like a pamphlet (the bottom third will be both dough and butter.)
The dough is now a horizontal rectangle. Turn it one quarter turn clockwise, so that it is now a vertical rectangle. Gently push with a rolling pin a few times along the length of the dough to help work in the butter.
Roll the pastry out into another 20 x 30cm rectangle and fold it once again into a pamphlet.
Turn the pamphlet 90 degrees and roll it out again into a 20 x 30cm rectangle, and fold it up into a pamphlet. That was two turns and rolls in total. Now the folded dough needs to rest in the refrigerator for at least 20 minutes. After 20 minutes remove it from the refrigerator and lay it out on the bench so it is a vertical rectangle. Roll it out again into a 20 x 30 cm rectangle and repeat the folding, and rolling to complete another two turns. Chill the dough for 20 minutes.
Repeat this process one more time, so in total the dough was turned and rolled a total of 6 times.
At this point the butter should be incorporated into the dough and there shouldn’t be visible clumps remaining. If there are still clumps, your butter may be too cold. Perform another set of turns for a total of 7 turns. Any more than that and you may overwork the dough.
After all the turns are completed, let the dough chill for a minimum of 2 hours in the refrigerator before rolling out once more and baking. Alternatively it can be frozen for up to 4 months to use at a later date. If you’re freezing it, let it thaw, but not heat up, before rolling out.