Clean the dock leaves of the tough parts (midribs) and put them to parboil for about 15-20 min. in boiling water. Then drain them from the water with a slotted spoon and add all the remaining products to it, with the onions chopped finely.
Stir everything well in a large and deep bowl, so that all the ingredients mix well. Once you're sure that that is the case, pour it into a suitable baking dish.
Distribute the mixture evenly and form a level surface. Bake until slightly reddened in a preheated 482°F (250° C) oven.
You don't need to follow the ingredient quantities precisely in this recipe, it's more a matter of taste. Taste it and adjust them as desired.