Scrub clams well with a brush; discard opened or cracked clams or any heavy ones (indicating they're filled with sand).
Heat oil and butter in a Dutch oven over medium heat. Add prosciutto; cook, stirring often, 5 minutes or until browned. Add garlic and red pepper; cook 2 minutes. Add wine, lemon rind, and thyme; bring to a boil. Add clams; cover and cook, stirring occasionally, 3 to 6 minutes or until clams open. Spoon into individual bowls. Sprinkle with parsley. Garnish, if desired.