Most Japanese cooks rely on prepared curry bricks to make curry. These are basically blocks of seasoned roux—the shape of a chocolate bar—made of spices (including turmeric, coriander, cumin, and fennel), salt, flour, and butter that can be dissolved in water to make an instant curry sauce. My brick is on the mild side, so if you like it spicier, add the cayenne pepper. To make your curry block gluten-free, chickpea flour is a good alternative that is used in Indian curries. If using chickpea flour, it will be soupy in consistency. You can add a tablespoon of mochiko (glutinous rice flour) diluted with equal amounts of water to thicken the curry.
One curry brick in this recipe makes about three batches of Japanese-style curry. You can break up the brick into three pieces and store it in the refrigerator. This recipe makes more curry powder than you will need for the brick. You can use the remaining powder to sprinkle on vegetables and salads or save it for the next batch of brick.