Place a large, deep skillet over medium heat.
Add the sugar and 2 tablespoons (30 ml / 1 fl oz) of water.
Cook without stirring, gently shaking the pan occasionally, until the sugar melts and begins to bubble, about 10 minutes.
Continue cooking until the liquid sugar turns a deep amber color. Immediately turn off the heat to prevent burning.
In a separate bowl, mix the vegetarian fish sauce with 1/2 cup (480 ml) of water. Standing back at arm's length, carefully pour this mixture into the hot caramel. It will bubble and seize violently.
Turn the heat back to medium-high and stir constantly until the hardened caramel fully dissolves into the liquid, creating a smooth sauce, about 2 minutes.
Add the sliced shallots to the sauce and cook, stirring occasionally, until they soften, about 5 minutes.
Stir in the black pepper and a squeeze of lime juice. Gently add the tofu cubes to the skillet, ensuring they are coated in the sauce.
Bring to a simmer and cook for about 5-7 minutes, stirring gently, until the tofu is heated through and has absorbed some of the sauce.
Taste the sauce and adjust the seasoning with more lime juice for acidity or black pepper for heat.
Garnish generously with fresh cilantro and serve immediately with steamed rice.
When making the caramel, resist the urge to stir it with a spoon as it can cause crystallization. Instead, gently swirl the pan to ensure even heating. Watch the color closely—it can go from perfect to burnt in seconds.
Don't be shy with the black pepper. It's a key component of this dish, providing a warm, spicy counterpoint to the sweet and savory sauce. Freshly cracked pepper makes a world of difference.