How to Make It
Preheat the oven to 450°. In a small saucepan, bring 3/4 cup of water to a boil. Stir in the dashi powder until dissolved.
In a large pot, bring 2 1/2 cups of water to a boil. Add the clams, cover and cook over moderately high heat for 5 to 7 minutes; transfer to a baking sheet as they open, and discard any that don’t. Strain 3/4 cup of the clam cooking liquid into a large saucepan. Add the dashi, apple cider, fish sauce, white soy sauce and tobanjan to make a clam broth.
In a medium skillet, melt the butter. Add the capellini and toast over moderately high heat, stirring, until golden, 3 to 4 minutes. Add half of the clam broth and layer the cabbage, garlic, ginger, leek and serrano chile on top; do not stir. Bake for about 15 minutes, until all of the broth is absorbed and the pasta is al dente.
Add the steamed clams to the remaining broth in the saucepan. Stir in the escarole and simmer until heated through. Stir in the oregano. Transfer the pasta and vegetables to bowls, top with the steamed clams and escarole and serve.
Dashi powder is available at many health food stores and at Asian markets. White soy sauce, also known as shoyu, and tobanjan, a spicy, fermented bean paste also known as doubanjiang, are available at Asian markets, too.