Sift flour and in a well in the middle, add the baking soda, vinegar and oil. While adding a little water, knead a soft dough, which can be rolled out. Roll it out into 2 thick sheets and let them sit for a while to dry a bit. Parboil the nettle in boiling water and drain it.
In 3-4 tablespoons of oil, sauté the finely chopped onion, adding 1-2 tablespoons of water. Once softened, add the chopped spearmint, nettle and season to taste with black pepper and salt. In a greased tray, place one sheet, put the filling on top and cover with the second sheet.
Sprinkle the top of the pie with preheated oil. Put it to bake in a moderately heated 356°F (180 °C) oven. Remove it and smother it in a towel.