Sift the flour onto a wooden board (you may use the stand electric mixer fitted with the dough hook);
Sift in salt and baking soda;
Add lard or oil. Smash the lard with the tips of your fingers and combine it with the flour until it is completely incorporated;
Mix with a fork taking the flour from the sides a little at a time; then add water gradually. Start mixing with your hands until the dough comes together. Add more flour in case of sticky dough;
Knead vigorously until a smooth and elastic dough;
Divide the dough into 8-10 even balls; they should be as big as a tangerine (about 150-160g each). Knead until a dough;
Place the balls to rest for at least 2 hours (you may use the dough without letting it rest, but it will result less tasty);
Flour the pastry board and place the first ball;
On a smooth surface (a marble surface is perfect), roll the ball into a disc roughly 20-25cm in diameter and 2mm thick. Try to make it as round as possible: keep the rolling pin always in the same position while you are rolling the ball. Rotate at the right angles the dough, instead.
If the piada sticks to the rolling pin, sprinkle the surface with a little flour;
Heat a griddle pan, a non-stick pan, or even a refractory plate; cook the piadina over medium heat;
Gently prick the surface to avoid bubbles;
It takes a few minutes; cook the piadina a couple of minutes on each side or until it gets golden; use a spatula to flip it over. Piadina is done when it shows leopard-like spots.
Add the filling to your taste. Read below for a few hints.