In a bowl, add the cubed 40g of butter, all-purpose flour, bread flour, and salt. Use your fingers to rub the butter into the dry ingredients until it is in small pieces.
Create a well in the center of your mixture, pour in the cold water and vinegar, then cut through with a spoon or a dough scraper.
Dump the dough onto your counter and knead for approximately 5 minutes.
Flatten dough into a rectangle (as you can), cover in plastic wrap, and place in the fridge for 30-40 minutes.
Lightly flour the counter and roll your dough to 18cm x 36cm. Be sure to “feather” your dough - lifting it from the counter and flipping it over after every roll - so it doesn’t stick or tear. Very lightly dust with flour if needed, as you roll.
Cover your dough with plastic wrap and stick it back in the fridge while you prep your butter square.
Create an 18cm x 18cm enclosed parchment square. Fold a piece of parchment in half, 18 centimeters wide when folded, and then fold over the excess on all other sides to have an enclosed square.
Place your 210g block of butter between two butter wrappers and flatten it down with a rolling pin. Wacking it 3-4 times* to get it shaped into a flatter rectangle. Then place inside the middle of your 18cm x 18cm parchment square, fold the parchment closed, and roll the butter out flat, evenly filling the square.
Remove your dough from the fridge and place your butter square into the center of the dough, dust off any excess flour on the inside of the dough.
Fold the top half of the dough down to the middle of the butter square and the bottom half of the dough up to the middle, having the two seams meet. Gently pull the dough to shape as needed, so the seams evenly meet and the butter is covered. Pinch the dough seam together.
Turn the dough 90 degrees from where originally rolled. Minimally flour your counter and the top of the dough square
Gently press down with a rolling pin from top to bottom, to begin to help stretch the dough vertically, then flip over (keeping the dough in the same vertical direction) and press down again.
Roll from the middle of the dough downward and then the middle of the dough upward - feathering in-between - until the dough is 60 cm long.
Lightly dust with flour as needed between full rolls. Be sure to observe your dough as you roll it. You can roll it past 60cm, but if it starts retracting, it doesn’t want to be stretched further, so don’t push it.
Once your dough is the right length, dust off any excess flour from the side facing up.
Perform an envelope fold. Fold the dough ⅓ down, brush off excess flour from the side facing up, then fold the bottom ⅓ up (covering the dough you just folded down). Make sure all parts are evenly covered.
Turn the dough 90 degrees, so your folds are now facing the side, wrap it in plastic, and place it in the fridge. This is your first turn. Refrigerate the dough for 30-40 mins.
Once the refrigeration time is up, use a thermometer and stick it gently between your envelope folds to make sure your butter is between 52-61°F (11- 16 °C) before rolling. It’s very important that your butter is neither too warm nor too cold, or it could mess up your layers.
You will need to do three turns in total. After your first turn above, roll again to 60cm, envelope fold, and refrigerate for 30-40 mins. Repeat one more time after this for your third turn.
Once you’ve completed all three turns and refrigeration, congrats, you have puff pastry dough to use as you please*!