Preheat oven to 400. Wash and dry potatoes. Poke a couple small holes in each potato with a fork. Rub each with a bit of olive oil and sprinkle with salt and bake for 30-45 minutes until it's easy to pierce with a fork.
Thinly slice onions from root to stem. Heat a large aluminum or cast iron frying pan over medium heat and warm 2 tbsp oil and 2 tbsp butter. Add onions to pan and mix. Cook for 5 minutes, then add a pinch of salt. Cook down for 25-35 minutes until onions are deeply golden brown, stirring every 5 minutes.
Once onions are deeply golden brown, turn heat back up to medium high. Add 1 tbsp minced garlic, 1 tbsp fresh thyme and cook for 1 minute. Add 1 cup beef stock and mix well, then add ½ tbsp balsamic vinegar. Bring to a simmer and cook until most of the liquid is gone - about 2 minutes.
Take your baked potatoes and slice the top ¼ off lengthwise. Scoop out inside into a bowl. Add onions, 2 tbsp heavy cream, and ½ cup shredded gouda and mix well. Re-stuff potatoes, so the stuffing is slightly sticking out the top. Bake for 10 minutes.
Remove from oven and top each potato with more shredded gouda and bake until cheese is golden brown. Top with fresh thyme and enjoy.
