In a large stockpot, add the mushrooms and ¼ cup (60 ml) of water. Simmer the mushrooms in the water until the water has almost cooked off. Add 1 tablespoon (15 ml) of the olive oil and sauté until the mushrooms are just beginning to brown, 3 to 5 minutes. Remove the mushrooms from the pot.
Add the remaining 2 tablespoons (30 ml) of olive oil to the stockpot and heat until shimmering. Add the onions and salt and reduce the heat to low. Cover the stockpot and allow the onions to cook for 10 minutes. They will soften and become translucent.
Then, remove the cover and continue to slow cook the onions for an additional 10 to 15 minutes, stirring occasionally. They will turn a rich brown color. Then, add the garlic and continue to cook for 1 to 2 additional minutes.
Add the tomato paste and increase the heat to medium. Sauté the tomato paste until it becomes a dark red, 2 to 3 minutes. Add the tamari sauce and maple syrup and continue sautéing for 1 to 2 minutes. The maple syrup should begin to thicken.
Add the mushrooms, carrots, turnips and 1 cup (240 ml) of water to the pot. Stir to combine. Simmer, covered, for 30 to 35 minutes, stirring occasionally, until the root vegetables are easily pierced with a fork.
The broth should have cooked down to a thick sauce. If the sauce is too thin, continue to simmer, uncovered, for about 5 minutes.
Serve with the fresh ground pepper.