Wrap the tofu in a thin dish towel or a few paper towels and press for 10 to 15 minutes.
Slice the tofu in half vertically, then flip each slab around and slice crosswise into squares about ½-inch (1 to 1.5 cm) thick.
Arrange the tofu in a single layer on a cutting board. Gently press down on the squares with a towel to release more water. Sprinkle the tofu with a couple of pinches of salt. Line a large plate with a few paper towels.
Heat a 12-inch (30 cm) nonstick skillet over medium-high heat for 2 minutes, then add the oil and heat for 30 seconds. Carefully add the tofu, arranging it in a single layer.
Move the tofu around in the oil to evenly coat it and cook until golden brown on the bottom, 5 to 7 minutes. Use a thin spatula to flip and cook until the other side is also golden brown, 4 to 5 minutes.
While the tofu cooks, make the braising liquid. Use the back of a large knife or a sturdy mug to roughly crush the coriander seeds. Or you can use a mortar and pestle or pulse once in a spice grinder.
In a medium (2-quart/2 L) heavy-bottomed saucepan, combine the coconut milk, soy sauce, agave, lemongrass, ginger, garlic, chiles (if using), roughly crushed coriander, white pepper, and cinnamon. Bring to a boil, stirring occasionally, then reduce the heat and simmer for 7 to 8 minutes. It should be very flavorful and quite salty.
Add the fried tofu to the braising liquid and stir to coat. A few pieces of tofu will peek up above the liquid, but that’s okay. Simmer gently, stirring occasionally, until the tofu is almost wrinkly and the liquid has thickened into a sauce that sticks to the tofu, about 35 minutes.
Remove from the heat and let cool briefly; discard the cinnamon stick. Serve over rice, pour a little braising liquid on top of the rice (not a lot, as it’s quite potent), and garnish with sesame seeds and herbs.