PreparationMake dashi: Simmer mushrooms in water in a small saucepan 5 minutes, then let steep off heat 10 minutes. Add kombu and return just to a simmer. Turn off heat and add bonito flakes, then let steep 10 minutes. Strain stock through a fine-mesh sieve into a bowl or glass measure, discarding solids. Cool dashi to room temperature. Make custard: Beat eggs and 1 1/2 cups cooled dashi in a medium bowl, then whisk in remaining custard ingredients. Divide among bowls. Cover each tightly with foil and arrange in a steamer rack. Steam, covered, over simmering water until just barely set in center, 8 to 10 minutes. Remove pot from heat and let stand, covered, 2 to 3 minutes. (Custard will continue to set.) Prepare crab topping while custard steams: Blanch chives in a medium pot of boiling salted water 30 seconds, then transfer to an ice bath to stop cooking. Pat chives dry. Cut into 3/4-inch pieces and gently combine with crab and remaining ingredients. Top warm custards with crab mixture. Cooks' note:Dashi can be made 1 day ahead and chilled.
PreparationMake dashi: Simmer mushrooms in water in a small saucepan 5 minutes, then let steep off heat 10 minutes. Add kombu and return just to a simmer. Turn off heat and add bonito flakes, then let steep 10 minutes. Strain stock through a fine-mesh sieve into a bowl or glass measure, discarding solids. Cool dashi to room temperature. Make custard: Beat eggs and 1 1/2 cups cooled dashi in a medium bowl, then whisk in remaining custard ingredients. Divide among bowls. Cover each tightly with foil and arrange in a steamer rack. Steam, covered, over simmering water until just barely set in center, 8 to 10 minutes. Remove pot from heat and let stand, covered, 2 to 3 minutes. (Custard will continue to set.) Prepare crab topping while custard steams: Blanch chives in a medium pot of boiling salted water 30 seconds, then transfer to an ice bath to stop cooking. Pat chives dry. Cut into 3/4-inch pieces and gently combine with crab and remaining ingredients. Top warm custards with crab mixture. Cooks' note:Dashi can be made 1 day ahead and chilled.