Thinly slice onion. Add to a pan over medium-high heat with salt, water, and oil. Stir and cover with a lid to steam for about 15 mins, until the water has evaporated.
1 ½ sweet or yellow onion, ½ teaspoon salt, ⅓ cup water, 1 tablespoon oil
Add garlic, sage, and thyme, and sauté until the onions are caramelized and brown. This is easiest done if you leave the onions in a single layer without stirring, and flip them over when they start to brown. This will take at least 10 more mins.
3 cloves garlic, 1 tablespoon fresh sage, 2 tablespoon fresh thyme
Once your onions are caramelized, add the mixture to a blender, along with, cornstarch, vegetable broth, tamari, and umami seasoning. Blend until it is extremely smooth and no lumps remain.
2 tablespoon cornstarch, 2 ½ cups vegetable broth, 2 tablespoon tamari or soy sauce, 1 teaspoon mushroom umami seasoning or mushroom powder
Return the blended mixture to a saucepan and bring to a soft simmer, to heat and thicken, before serving. If you want, you can thin it out by adding water 1 tablespoon at a time until you reach your desired consistency. Remove from heat and serve!