This caramelized onion dip will be the hit of the party. Be patient while caramelizing the onions, time is the secret ingredient to caramelizing the onions to become super sweet and jammy.
Melt the butter with the canola oil in a large cast iron or heavy bottomed skillet over medium high heat. Add the onions and sprinkle with 1 teaspoon of the kosher salt and fresh thyme leaves. Cook the onions for 5 minutes or until they start to soften, stirring so they don't crisp or brown in spots. Reduce the heat to medium low, cover with a lid, and continue to cook for 30 minutes, stirring the onions every 10-15 minutes or so. Add the additional 1 teaspoon of salt and the soy sauce as the onions reduce and become more golden and jammy, giving off a rich nutty aroma. If the onions look like they're beginning to burn or crisp, stir in a splash of water or broth and scrape the caramelized fond from the bottom of the pan for the onions to absorb. Remove from the heat and cool.
Mix the greek yogurt with the sour cream and onion powder in a medium bowl. Stir in the cooled onions and refrigerate for 30 minutes up to 3 days before serving.