Whisk together the eggs and milk in a bowl until evenly blended. Mix in the zucchini, razor clams, onion and garlic; set aside. Stir together the bread crumbs, flour, parsley, salt and pepper in a separate large bowl. Pour the egg and vegetable mixture into the flour mixture and stir until well combined.
Heat oil and butter in a large, deep frypan over medium-high heat. Drop fritter batter by spoonfuls into the frypan in batches of 4. Cook until golden brown on the bottom; flip and cook until the other side is golden brown. Drain the fritters on a paper towel-lined plate.