Slice the block (or blocks) of tofu into small equal cubes. Line a large cutting board with paper towels, arrange the tofu cubes all over the board in an even layer, cover them with more paper towels, then another cutting board. Place something heavy on top - like a cast iron skillet or jars filled with flour.
Let the tofu sit like that for 15 minutes. If needed, change the towels halfway through, if they get too wet during the process. As the tofu drains, preheat the oven to 400°F (200°C) and line a large baking sheet with parchment paper. Set aside.
Once the tofu is drained, transfer it to a large mixing bowl and coat it with tamari. Then stir in oil until all tofu is coated. Sprinkle with 1 tablespoon cornstarch and toss tofu until it’s completely coated, without any cornstarch left. If you spot any uncovered areas, add more cornstarch.
Transfer tofu to baking sheet and bake for about 20 minutes, until tofu is golden (golden brown on the edges).