Preheat the oven to 350 degrees F.

To make the sauce, melt the butter in a saucepan over medium-high heat. Add the onions and cook, stirring, for 3 minutes. Add the garlic and cook, stirring, for 1 minute. Add the tomatoes and chicken stock. Simmer, stirring occasionally, for 5 minutes. Add the vinegar and simmer, stirring occasionally, until the sauce thickens, about 5 minutes. Remove from the heat and adjust the seasoning, to taste.

Separate the cabbage leaves and remove the hard spine from each leaf. Spread on paper towels and pat dry. Set aside.

To make the stuffing, in a medium skillet melt the butter over medium-high heat. Add the onions and cook, stirring, until very wilted and starting to caramelize, about 5 minutes. Add the garlic, and cook, stirring, until for 1 minute. Remove from the heat and let cool slightly.

Lay the cabbage leaves, rib side down, on a flat work surface. Remove rib or shave down leaf to make leaf easy to roll.

In a large bowl, combine the beef, pork, rice, eggs, Essence, salt, pepper, and cooked onions. Mix well with a heavy wooden spoon or your hands.

Line a large baking dish or roaster with remaining cabbage leaves.

One at a time, spoon the filling into the center of the cabbage leaves, about 1/4 cup in each, depending upon the size of the leaves. Roll each into a neat cylinder and place in a single layer in the baking dish. Repeat with the remaining ingredients, stacking the cabbage packages, as necessary. Pour sauce over the rolls, cover tightly with aluminum foil, and bake until the meat is cooked through and the rolls are tender, about 2 hours.

Remove from the oven and serve the rolls with any remaining sauce spooned over the top, if desired.