Cut the mochi into bite-sized pieces. Thinly slice the onion and trim the base of the shimeji mushrooms, separating them.

Heat salad oil in a frying pan over medium heat. Add the onion and shimeji mushrooms, and sauté until softened.

Add the peeled shrimp to the pan and sauté briefly until they turn pink.

Turn off the heat and mix in the flour until no powdery texture remains.

Reheat the pan and add milk, salt, and pepper. Simmer over medium-low heat for 3–4 minutes until the mixture thickens.