In a medium saucepan, combine dashi stock, soy sauce, mirin, and salt. Bring to a gentle simmer for 3–4 minutes.

In a skillet, sear chicken thighs over medium-high heat until golden brown, then add sliced shiitake mushrooms and sauté until tender.

In a separate pot, boil water and cook udon noodles for 2–3 minutes, then drain and rinse with warm water.

Divide the cooked udon noodles into bowls and ladle hot dashi broth over them. Top with sautéed chicken and mushrooms.

Place tempura shrimp and a soft-cooked egg on top of each bowl. Cover with a lid and let sit for 1 minute.

Garnish with green onions and optional spinach or kamaboko, then serve immediately.