Mix the flour with the salt and rub in half of the lard. Add enough cold water to bring the flour to a soft dough.
Mix together the rest of the lard and the butter.
Roll out the dough to make a rectangle 12.5 x 25cm/5 x 10in.
Dot one third of the butter/lard mixture over two-thirds of the rectangle. Fold the third without any fat on it over the middle third of the pastry. Bring the other third on top. Seal the edges with a rolling pin and turn the dough 90 degrees. Chill for 10 minutes.
Repeat stage 4 with half of the rest of the fat and then repeat one more time with the remaining fat. Chill for 10 minutes after each folding.
Roll and fold one more time without any fat and then chill for 30 minutes.