Scrub the clams before cooking to remove any sand on their shells. Eastern littleneck clams average eight to 10 clams per pound. You can substitute other small, hard-shelled clams, such as Manila clams, cockles, or Pacific littlenecks, but their sizes (and the number of clams per serving) and cooking times will vary. Do not use larger clams, such as cherrystones or quahogs, or soft-shelled clams. This recipe can easily be doubled in a Dutch oven; increase the cooking time for the clams to about 12 minutes.
Whisk cornstarch into wine in liquid measuring cup until dissolved; set aside. Combine chorizo, oil, and garlic in 12-inch skillet. Cook over medium-high heat until garlic begins to brown around edges and chorizo begins to render its fat, 3 to 4 minutes.
Whisk wine mixture to recombine. Add clams; pimentos, if using; and wine mixture to skillet and bring to boil. Cover and cook until clams open, 8 to 10 minutes. Remove from heat and use tongs or slotted spoon to transfer clams to deep platter. Stir parsley into sauce and pour sauce and chorizo over clams. Serve with bread.
