Step 1 Scrub the clams under running water with a small brush to remove any sand or dirt. Place the clams in a large saucepan and add 1 1/2 cups of the water. Cover the pot and heat over high heat until the water is boiling and steam comes from the pot. Turn off the heat. At this point the clams should be open. If they are not open, continue to cook another minute or so until they open.
Step 2 Remove the clams from the broth. Strain the broth through a cheesecloth and measure 1 cup for the soup. Use the remaining broth for another recipe or freeze for future use.
Step 3Combine the remaining 4 cups of water and the dashi in a saucepan and heat to boiling. Stir in the reserved 1 cup of clam broth and miso until blended.
Step 4Divide the clams among 4 shallow serving bowls. Pour the broth over them, dividing evenly. Sprinkle each serving with the snipped chives.
Step 5Garnish with a daikon curl and a few chives.