Begin by caramelizing you onions (these can be made ahead). Add olive oil to a standard-size cast iron skillet over medium low heat. Add sea salt and sauté for 5 minutes, until golden. Stir to prevent sticking. Cover your skillet, turn heat to low, and let onions steam for 25-30 minutes. Check occasionally to ensure they're not burning, adding a splash of water if needed. This process will take some time so try not to check too often! I use the lowest heat possible on my stovetop.

Remove the lid and deglaze the pan with white wine. Stir to let wine reduce. Repeat this process with the balsamic vinegar. Stir and add minced garlic, dried thyme, and optional red pepper. By this point your onions have been cooking for nearly 45 minutes, should be a dark brown and smell sweet. Turn off heat but leave onions in pan.

To make white sauce, add slivered almonds, nutritional yeast, apple cider vinegar, and almond milk to a high speed blender and combine until smooth. Add a splash of water if needed to help things along. The sauce should not be grainy at all, but velvety and smooth. Set sauce aside.

Turn heat to medium. Add to pan chopped mushrooms and let cook for 2 minutes until some of their natural water is released. One the mushrooms are looking browned, add 2 cups water or broth (slightly less if your skillet is less than 12 inches across and 2 inches deep), parsley, and your reserved sauce. Bring mixture to a heavy simmer/near boil in the pan, watching carefully for overflow.

Break lasagna sheets and poke inside the mixture so that they are covered by liquid. Let entire mixture simmer on high until noodles are cooked (about 10 minutes). You may want to cover the skillet with a lid to ensure the pasta cooks through fully. Remove from heat, let cool slightly, and serve.