Drain oysters, reserving 3/4 cup liquid.
Melt butter in a skillet; add shallots, and sauté until tender. Whisk in flour; cook, whisking constantly, 1 minute. Gradually add reserved oyster liquid and half-and-half; cook over medium heat, whisking constantly, until thickened and bubbly. Add oysters, and cook 5 minutes or until done. Stir in salt, pepper, and vermouth. Garnish, if desired; serve immediately.
NOTE: This oyster stew recipe is typical of those made in the South.