Instead of buying firm tofu, why not try making it yourself? This is called tezukuri momen-dofu.
Ingredients
7 oz dried soybeans
2 tsp nigari (coagulant)
method
Soak the beans in 4 1/2 cups water for 10-20 hours, depending on the humidity in the air.
Dissolve the nigari in 6 tbsp room temperature spring water
Grind the soybeans still in the water for 2 minutes, until fine.
Boil 5 cup of water over medium, then add the soybean grounds, continuously stirring. Before it comes to a boil, reduce heat to low. Cook for another 8 minutes, stirring.
Strain through finely woven cotton cloth into a pot. The liquid draining is soy milk, and the stuff left in the cloth is the pulp, called okara. You can reserve the okara as a topping for rice.
Cook the soy milk over low, removing once the temperature is 155F
Add half of the nigari to the soy milk, stirring continuously, then add the rest, stirring in a figure eight.
When the milk begins to coagulate, cover and let stand for 15 minutes.
Place a tightly woven cotton cloth in a strainer and set over a bowl. Gently ladle the milk into the strainer and then fold the cloth over to cover the milk. Place a 1 lb weight on top to help drain.
After 15 minutes, the milk will be firm. Place in a bowl of ice water gently, and let cold water run over it, careful not to hit the tofu directly as this will break it. Serve!
You can try it freshly made and cut into bite sized cubes topped with finely sliced green onion and a pinch of grated ginger, some soy sauce poured over it.
You can also chill it for later use, when you can cut into bite sized cubes and cover it with tempura batter to make agedashi tofu, served partially submerged in a pool of tempura dipping sauce. delicious!