Dissolve the sugar and yeast in 1 cup (250 ml) warm water. Leave it aside for 10 min. In the meantime, sift the flour and then mix it with the salt, yeast and oil. Knead a dough, smear it with oil and put it in a 122°F (50 °C) oven to puff up.
While you're waiting for that to happen, make the filling. Chop the onions and leeks, saute them in a little oil. Once they change color, add the tomatoes and spices to them. Stir and turn the stove off.
Divide the risen dough into 2 parts - make one of them smaller. Roll out 2 sheets from them. Lay out the larger one in a buttered oven dish, with its edges sticking out. Distribute the filling on top and place the 2nd dough sheet. Cover it with the edges of the lower sheet that stick out.
Put thus prepared onion pie in a preheated 122°F (50 °C) oven dish to rise for another 15 min. Then bake for 30 min. at 356°F (180 °C).