Heat 1/2 cup olive oil, in a frying pan and saute the onions unitl soft. Add rice and cook, covered, for 5 minutes. Add all remaining ingedients, except grapevine leaves, lemon and 1/2 cup olive oil. Simmer for 5 minutes. Cool. Rinse the grapevine leaves in cold water. If fresh, drop them in boiling water and boil for 3 minutes. Strain and rinse in cold water.
In the center of each leaf, shiny surface of leaf down-wards, place a heaped teaspoon of the filling. Fold ends of leaf over the filling and roll it up. (Do not roll too tighly as the rice will swell). Cover the bottom of a shallow saucepan with vine leaves and place "dolmathakia" side by side in layers. Sprinkle with lemon juice, add 1/2 cup olive oil and 1 1/2 cups hot water. Place a plate over "dolmathakia" to prevent them from opening, cover and simmer over a low heat for about 1 hour. Allow to cool in the saucepan. Serve them as a cold entree.