On a sheet of wax paper, roughly form an approx. 6" square with the butter block mixture. Lay another piece of wax paper on top and smooth out the square & straighten the sides. Peel back each wax paper sheet & re-lay as it wrinkles to keep a smooth, even surface. After block's thickness & sides are even, refrigerate until firm.
Shape into a mound, then make a well in the center of the mound. Add the salt & cold water into the well, then with a fork, use a whisking motion to gradually incorporate the well's sides into the water. When it starts to form a solid mass, finish incorporating the flour by kneading. Incorporate just until it is still sticky and has a rough texture. Adjust the water & flour as needed. Try to knead as little as possible. Puff pastry likes lazy kneaders.
Form dough into a ball, remember-knead as little as possible. Flatten the ball a bit, then cut a cross halfway through the dough. Wrap it up & let rest in fridge for 30 minutes.
Place the butter block diagonally on the dough square, so that the butter corners are pointed at the middle of the dough sides. Fold the uncovered dough corners over the butter block to completely envelop the butter. Pinch the seams tightly together to seal in the butter.
Dust your work surface with flour, and roll the dough into a rectangle about 1/2" thick. Remember to keep dusting with flour whenever needed to keep the dough from sticking & tearing the layers.
Size up your rectangle visually into 3. Fold one third over the middle, then fold the opposite third over. Just like a tri-fold brochure. Try to have everything as even as possible. All the edges should match fairly closely. Put on a plate, cover, and refrigerate for about 30 minutes. Relax, read the paper, check email, whatever you like.
Roll out to 1/2" thick and repeat the fold. Don't forget to flour as you roll. Plate, cover, and refrigerate for 30 minutes. Repeat this for a total five roll & folds.
After the last fold, roll the rectangle out to about 3/4". If it is difficult, put dough in the fridge for a bit to relax the gluten. If using immediately, cover, rest in fridge for about 30 minutes, then use as needed. If it's for later, cut into sections big enough but that still fit easily in your freezer (usually just in half), layer with wax paper between sections, freezer bag it, & store until needed.