Peel shrimp, reserving shells; devein, if desired.
Melt 1 tablespoon butter in a 3 1/2-quart saucepan over medium heat. Add shrimp, and cook 5 minutes or just until shrimp turn pink. Chop shrimp, and set aside.
Add shrimp shells, shallot, and chicken broth to saucepan; bring to a boil. Remove from heat, cover, and let stand 30 minutes. Pour broth mixture through a wire-mesh strainer into a bowl, discarding shells and shallot.
Melt remaining 1 1/2 tablespoons butter in saucepan over medium heat. Whisk in flour. Cook, whisking constantly, 1 minute. Gradually whisk in broth mixture. Bring to a boil; boil 1 minute or until slightly thickened. Add cream; reduce heat to low. Add chopped shrimp and sherry; stir until thoroughly heated.