Part 1: Prepare and Crisp the Tofu

1. Press the Tofu: This is the most crucial step for non-soggy tofu. Remove the tofu from its packaging and drain the water. Wrap the block in several layers of paper towels or a clean kitchen towel. Place it on a plate and put something heavy on top, like a cast-iron skillet, a few cookbooks, or a cutting board weighed down with cans. Let it press for at least 30 minutes, or up to an hour. You’ll be amazed at how much water comes out.
2. Cut the Tofu: Once pressed, unwrap the tofu and cut it into 1-inch cubes.
3. Marinate and Coat: In a medium bowl, add the tofu cubes, 1 tablespoon of soy sauce, and 2 tablespoons of cornstarch. Gently toss with your hands or a spatula until each cube is evenly and lightly coated. The soy sauce helps the cornstarch stick, and the cornstarch creates an incredibly crispy crust.
4. Pan-Fry the Tofu: Heat 2 tablespoons of neutral oil in a large skillet or wok over medium-high heat. Once the oil is shimmering, carefully add the coated tofu cubes in a single layer. Be sure not to crowd the pan; cook in two batches if necessary.
5. Achieve Golden Perfection: Fry the tofu for about 3-4 minutes per side, until all sides are golden brown and crispy. Use tongs to turn the cubes. Once cooked, remove the tofu from the skillet and set it aside on a plate lined with a paper towel.

Part 2: Whisk Together the Stir-Fry Sauce

1. Combine Ingredients: While the tofu is frying, prepare your sauce. In a small bowl or liquid measuring cup, combine all the sauce ingredients: low-sodium soy sauce, rice vinegar, maple syrup, toasted sesame oil, minced garlic, grated ginger, vegetable broth, and the 1 tablespoon of cornstarch.
2. Whisk Until Smooth: Whisk vigorously until the cornstarch is completely dissolved and the sauce is smooth. The cornstarch acts as a thickener, which will give your stir-fry a beautiful, glossy finish later on. Set the sauce aside.

Part 3: The Stir-Fry Assembly

1. Sauté the Aromatics: Wipe out the skillet you used for the tofu, or use a clean one. Add the remaining 1 tablespoon of oil and heat over medium-high heat. Add the sliced yellow onion and the white parts of the green onions. Sauté for 2-3 minutes until they begin to soften and become fragrant.
2. Cook the Mushrooms: Add all of the sliced mushrooms to the skillet. The key here is to let them cook without stirring too much initially. Spread them in a single layer and let them sear for 3-4 minutes until they release their water and begin to brown and caramelize. This develops a deep, meaty flavor. Continue to cook, stirring occasionally, for another 5-7 minutes until they are well-browned and tender.
3. Add Other Vegetables (If Using): If you’re adding broccoli or bell peppers, now is the time. Add them to the pan and stir-fry for 3-4 minutes until they are tender-crisp.
4. Combine and Sauce: Return the crispy tofu to the skillet with the vegetables. Give your prepared sauce a final quick whisk (the cornstarch may have settled) and pour it all over the tofu and vegetables.
5. Thicken the Sauce: Stir everything together gently to coat. The sauce will begin to bubble and thicken almost immediately due to the heat and the cornstarch. Cook for 1-2 minutes, constantly stirring, until the sauce has thickened to a beautiful, glossy consistency that clings to every piece of tofu and mushroom.
6. Final Touches: Turn off the heat. Stir in the green parts of the chopped green onions.
7. Serve Immediately: Serve your Tofu and Mushroom Stir-Fry hot, garnished with toasted sesame seeds and fresh cilantro if desired.