For an extra-special evening, make this carefully-stirred, decadent dish.
Heat stock in pan over high heat. Add clams; cover. Cook until opened, 5 to 10 minutes. Using a slotted spoon, transfer clams to a bowl. Discard unopened clams. Remove clams from shells, and chop clam meat. Add shrimp shells to stock. Cover; simmer 15 minutes. Pour stock through fine sieve, discarding solids and sand left in pan. Return stock to stove; keep at simmer over medium heat.
Heat oil in heavy-bottomed saucepan over medium heat. Add shallots and saffron; cook, stirring, until translucent. Add rice; cook, stirring, until rice begins to sound like glass beads, 3 to 4 minutes.
Add wine to rice. Cook, stirring, until wine is absorbed. Using a ladle, add 3/4 cup of hot stock to rice. Using a wooden spoon, stir rice constantly, at medium speed. When rice has absorbed most but not all of the liquid and mixture is just thick enough to leave a clear wake behind the spoon when stirring, add another 3/4 cup stock.
Continue adding stock in this manner, stirring constantly, until rice is mostly translucent but still opaque and slightly crunchy in center. Add shrimp; continue stirring and adding stock until rice is still al dente but not crunchy and shrimp is cooked through, about 3 minutes. As rice nears doneness, watch carefully, and add smaller amounts of liquid. The mixture should be thick enough that grains of rice are suspended in liquid about the consistency of heavy cream. It will thicken slightly when removed from heat.
Remove from heat. Stir in clams, butter, Parmesan cheese, if using, and parsley; season with salt and pepper. Divide among four bowls, and grate or shave Parmesan over risotto, if desired. Serve immediately.