Cream the yeast with 3 tablespoons (1/4 cup) of the liquid.
Mix the flours and salt together in a warmed bowl and make a well in the centre.
Pour in the yeast, lard and remaining liquid.
Draw enough flour into the liquid to form a thick batter.
Sprinkle some of the flour over this mixture and leave in a warm place for about 45 minutes, until spongy.
Do not knead, but mix together with a spoon or knife to the consistency of a soft paste.
Dust with flour and leave for 30 minutes in a warm place until well risen.
Turn onto a floured surface and roll lightly to a square, about 1 inch thick.
Place on a greased baking sheet and put into an oiled polythene (plastic) bag.
Leave for about 15 minutes.
Remove from the bag.
Bake in a moderately hot oven, 400°F, Gas Mark 6 for 15-20 minutes.
Cool on a wire tray.
When cold, cut into squares.