Preheat oven to 350. On stove, bring a pot of water to a boil.
Clean chard leaves and remove stems. Chop the stems into small pieces (1/4') and add to your mixing bowl.
Place the leaves in the hot water for just a few minutes to tenderize. Remove and place in a bowl of ice water.
Back to your mixing bowl, combine garlic, onion, thyme, oregano, chopped hazelnuts, feta cheese, beef, salt and pepper. Mix well with your hands and form into oblong meatballs, in the same quantity as leaves.
In your baking sheet, add tomato sauce, vinegar and sweeter, and stir together, spreading over the bottom of the pan.
Take each leaf (I find it helpful to dab on a paper towel), and placing meatball at the end, roll tight like a tortilla or spring roll. Set in baking sheet.
Once all leaves are rolled, cover dish with aluminum foil and bake for about 30 minutes.
Remove from oven and uncover. Top with white cheddar cheese and return to oven to melt.
Serve hot with a bit of the tomato sauce drizzled over. Enjoy!Great served with cauliflower rice!