Clean the sardines by removing the heads and bones.

Rinse them well, pat them dry, and dust with flour.

In a small skillet over medium heat, heat olive oil and cook the sardines until golden on all sides.

Transfer the sardines to paper towels to dry, reserving the oil.

Finally, transfer the sardines to an earthenware casserole dish or Dutch oven.

In the same skillet with the reserved oil over medium heat, cook the sliced onion and garlic until the garlic turns golden.

Add lemon peel, peppercorns, and bay leaves, then remove from heat.

Transfer this mixture to a small saucepan, and stir in vinegar, salt, and water.

Bring the mixture to a boil over high heat, then reduce the heat to low and simmer for about 5 minutes.

Pour the mixture over the sardines in the casserole dish.

Let it cool, and then refrigerate until 30 minutes before serving.