Preheat the oven to 250 degrees F. Line a baking sheet with parchment paper. Arrange the tomato slices on the baking sheet. Set the garlic, bread and almonds on and around the tomatoes. Drizzle all with the olive oil, and then bake for 90 minutes.
Place the roasted tomato mixture, ensuring you get all the juices from the pan, in a food processor. Add the peppers, vinegar and chili flakes. Pulse the mixture until smooth, adding a little more oil if too thick. Season the romesco sauce with salt and then transfer to a serving dish.
Season the steaks with salt and pepper. Lightly oil your grill. Grill the steaks to the desired doneness, and then plate and serve with the romesco sauce. Any leftover sauce can be refrigerated and used over the next few days. It makes a great dip or spread for a sandwich.
Recipe Options: Instead of top sirloin, serve the romesco sauce with any other tender steak, such as strip loin or rib eye. The romesco sauce could also be served with other meats, such as grilled chicken breast or pork tenderloin, or fish, such as roasted halibut. Instead of dried chilies, use a small, finely chopped, fresh jalapeno pepper in the romesco sauce.
Note: Roasted red peppers are sold in jars in the aisle where pickles are sold.