Work with the fish while still frozen (they will be easier to manipulate). To remove the scales, gently run the back of a knife along the skin under cold running water, making sure to keep it intact. Pat dry with paper towels.
Using scissors, remove the fins, then place the sardines flat on a work surface. Cut off the heads with a breadknife. Remove the fillets by cutting along the body, following the backbone. Gut each fillet and rinse, if needed. Pat dry with paper towels.
In a large skillet over medium-high heat, lightly brown the sardines, daisy capers, garlic and pepper flakes in the oil. Season with salt and pepper. Remove the sardines and set aside on a plate.
Add the tomatoes to the skillet and crush using a wooden spoon. Bring to a boil, cover with a splatter screen and simmer for 30 minutes or until the sauce has thickened. Return the sardines to the skillet. Adjust the seasoning.
Sprinkle with the fresh herbs and serve with fresh semolina pasta (see recipe), boiled potatoes or fresh bread.
Frozen sardines can be replaced with 2 cans (100 g) of oil- or water-packed sardines, drained. Skip steps 1 and 2 if using canned sardines.