Preheat the oven to 200C/400F on convection roast.
Peel and rinse the potatoes. If you have a proper crown potato grater, grate the potatoes directly into a bowl. Otherwise, cut the potatoes into pieces and purée them in the food processor. The purée shouldn't be perfectly smooth but still have some texture to it.
Add the milk and season the potato generously with salt and pepper. Mix everything together well.
Grease a baking pan well with the lard (or oil if you prefer). Pour in the potato batter. Dot the top with bits of lard or dizzle with oil.
Place the baking pan in the preheated oven either on the lowest rack or on the actual floor of the oven. Roast for about an hour or so, until the potato batter is cooked through and the bottom is nice and brown but (obviously!) not burnt. Since every oven is different, check on the progress from time to time starting about the 45 minute mark.
Now move the pan to the top rack and let it cook for another 10-15 minutes or so, until the top is golden brown as well.
Remove the baking pan from the oven and lay the torta on a cutting board. Cut into squares and serve while still warm.