Prepare the Tofu: Pat the tofu cubes dry with paper towels to remove excess moisture. Heat 1 tablespoon of vegetable oil in a non-stick pan over medium-high heat. Add the tofu cubes and fry until golden on all sides, about 5-7 minutes. Remove and set aside.

Sauté Aromatics: In a large skillet or wok, heat the remaining 1 tablespoon of vegetable oil and the sesame oil over medium heat. Add the minced garlic and sliced ginger and stir-fry for about 30 seconds until fragrant.

Cook Vegetables: Add the sliced shiitake mushrooms, carrot, and bell peppers to the skillet. Stir-fry for about 3-4 minutes until the vegetables are slightly softened.

Combine Sauces: Pour in the light soy sauce, dark soy sauce, and oyster sauce. Sprinkle with sugar, and stir well to coat the vegetables.

Add Stock: Pour in the vegetable stock or water, stirring to combine. Bring the mixture to a simmer.

Thicken Sauce: Stir the cornstarch mixture to recombine and add it to the skillet. Stir continuously until the sauce thickens, about 1-2 minutes.

Add Tofu: Gently add the fried tofu cubes back into the skillet, stirring carefully to coat the tofu with the sauce while preventing breakage.

Season to Taste: Taste the casserole and add salt and freshly ground white pepper to your preference.

Simmer: Lower the heat and let the casserole simmer for another 2-3 minutes to allow the flavors to meld together.

Garnish and Serve: Remove from heat, garnish with chopped spring onions, and serve the braised tofu casserole hot with steamed rice. Enjoy!