Prepare the dashi stock and allow it to cool to room temperature. Blanch the asparagus pieces and peas in boiling water for 2 minutes, then drain and set aside.

Season the chicken pieces with a pinch of salt. Divide the raw chicken, shrimp, and shiitake mushrooms evenly among 4 heatproof cups or chawanmushi bowls.

In a large bowl, gently whisk the eggs without creating too many bubbles. Add the cooled dashi, soy sauce, mirin, and salt. Whisk gently to combine.

Strain the egg mixture through a fine-mesh sieve to ensure a silky smooth custard. This step is essential for the perfect texture.

Carefully pour the strained egg mixture into each cup, filling them about three-quarters full. Gently tap cups on the counter to release any air bubbles.

Cover each cup tightly with aluminum foil. Place cups in a steamer over medium heat. Steam for 3 minutes on medium-high, then reduce heat to low and steam for an additional 18-20 minutes until the custard is set but still jiggles slightly. The internal temperature should reach 75°C to ensure the chicken and shrimp are safely cooked.

In the final 5 minutes of steaming, gently add the blanched asparagus and peas on top of each custard, re-cover, and continue steaming.

Remove from steamer and let rest for 2 minutes. Garnish with fresh chives and serve immediately while warm.