Place water in a large kettle fitted with a rack over high heat. Bring to a boil. Add clams; reduce heat to medium; cover and steam until clams open, 10 to 20 minutes. Remove clams from kettle; discard any that have not opened. Remove meat from clams; reserve. Strain cooking liquid through cheesecloth or coffee filter; reserve.
Heat oil in medium saucepan over medium heat. Add shallots; cook until almost tender. Add garlic; cook until golden. Add wine, parsley, butter, vermouth, and lemon juice. Reduce heat to low. Add 1-1/2 cups reserved clam broth; simmer 5 minutes. Add clams; heat through. Serve immediately, topped with toasted baguette slices and freshly grated Parmesan cheese.