Remove the tofu from the brine and pat with a paper towel to remove any excess liquid. Transfer into a tray and drizzle over the soy sauce and ponzu sauce. Leave to marinate for approximately 10-20 minutes.
In the meantime, heat 50g butter in a sauté pan. When foaming, add the shallots, and spinach and cook for 1-2 minutes until the spinach is wilted.
Remove from the heat and cover to keep warm.
Return the pan to heat and drizzle with some oil, add the marinated tofu and gently heat the tofu until caramelised on all sides.
In the meantime, toast the bread.
To serve, spread the rest of the butter on the toasted bread, add the warm spinach and the tofu. Top with a spoonful of hollandaise sauce and serve immediately.