Ad oil to a medium-sized pot. Place over medium heat.

When oil is hot and shimmering, add garlic, onions, carrots, celery and shrimp shells. Sauté until the vegetables lose their raw appearance and the shrimp shells turn red in color.

Add tomato paste. Sauté for 30 seconds, stirring constantly.

Add thyme, saffron, water, bay leaves and peppercorns. Bring mixture to a boil, then reduce the heat to a simmer. Continue to simmer for 20 minutes.

Remove from heat.

Strain the stock through a fine mesh sieve. Check the yield of the stock; you should have 4 1/2 cups. Should you have more, return the stock to a clean pot and keep reducing until it yields 4 1/2 cups. Should you have less, add water until it yields 4 1/2 cups.

Set aside until ready to use. Can be done in advance. Store in a tightly sealed container, in the refrigerator, until ready to use.