Let's prepare the ingredients. Cut the onion in half lengthwise and then slice into 1cm (0.4") slices across the grain. Slice the carrot into 4cm (1.6") slices and cut into 2mm (0.1") strips. Tear the shimeji mushrooms into small pieces. And slice the long green onion into 2cm (0.8") pieces.
Let's make the curry sauce for udon noodles. Add a small amount of vegetable oil to a pot and turn on the burner. Add in the white part of the long green onion sliced diagonally. Saute the onion to make it sweet and tender. When the onion is deliciously browned, remove and save it on a plate.
Add the vegetable oil again and reheat the pot. Add the onion, carrot and shimeji mushrooms. Lightly cook the ingredients. When the oil is distributed evenly, add in the beef slices. Continue to saute the ingredients.
When the redness in the meat has disappeared, reduce the heat to low. Then, add the curry powder. Stir-fry and bring out the aroma. The curry powder will easily burn so turn the heat off or maintain the lowest possible heat.
Now, pour the dashi stock into the pot. The curry has a strong flavor so you should use a relatively rich and savory broth to compensate. Add the sugar and usukuchi soy sauce. Combine the sauce. The usukuchi soy sauce helps to retain the presentable color of curry sauce but you can also use regular soy sauce.
Bring it to a boil on medium heat. Then, remove the foam. When the vegetables soften, reduce the heat to low. Thoroughly stir the diluted potato starch and add it to the broth a little at a time. If the heat is too strong, the starch will instantly clump up before it can be distributed.
Now, the sauce slightly thickens. Bring it to a boil on medium heat. Then, add the long green onion. Now, the curry sauce is ready.
Let's make the curry udon. Place the frozen udon noodles into a pot of boiling water. Loosen up the noodles. Then, boil for 30 seconds.
Remove the pot and quickly place the udon into a mesh strainer. Remove the excess water thoroughly and place the noodles into a bowl.
Pour the hot curry sauce over the udon along with the ingredients. Finally, top with the chopped spring onion leaves.
Usukuchi soy sauce is both saltier and lighter in color than regular soy sauce. It is often used in dishes that feature the colors of ingredients to help keep them from darkening.
Some people may have difficulties to find mirin so we intentionally made this recipe without using it. Hope more people can enjoy this delicious curry udon noodles!