Pour olive oil into a stock pot over medium-high heat. Add shrimp shells, thyme sprigs, garlic, bay leaf and dried shrimp (if using). Let sizzle for 1 to 2 minutes, stirring, taking care not to let mixture brown.
Add 7 cups water, bring to a boil, then reduce heat to a gentle simmer. Season to taste with salt and pepper. Simmer for 30 minutes. Strain through a fine-meshed sieve.
