Halibut in Hazelnut Romesco with Potatoes

Name: Halibut in Hazelnut Romesco with Potatoes
Ingredients: 1 large tomato (about 9 ounces); 1/2 cup husked toasted hazelnuts (about 2 1/2 ounces); 1/2 cup coarsely chopped drained piquillo peppers from jar or can; 4 tablespoons extra-virgin olive oil, divided; 2 garlic cloves, chopped; 1 1/2 teaspoons smoked paprika; 1 teaspoon Sherry wine vinegar or red wine vinegar; 1/2 teaspoon salt; 1/4 teaspoon cayenne pepper; 1 tablespoon unsalted butter; 4 6-ounce halibut fillets; 1/2 cup low-salt chicken broth; 12 baby Yukon Gold potatoes, halved, steamed until tendert; Chopped fresh parsley (optional)