For the sauce, combine bread and almonds in a food processor and process until finely ground. Add garlic, tomato, peppers, vinegar, salt and smoked paprika; process until puréed, stopping to scrape down the sides of the bowl once or twice. With the machine running, pour the oil through the feed tube. Transfer to a bowl.
For the beef, soak 12 small (6-inch) bamboo skewers in cold water for at least 30 minutes before cooking. In a large bowl, whisk together oil, garlic, sweet paprika, cumin, salt and cayenne. Add beef cubes, toss to coat, and set aside for at least 10 minutes, or refrigerate up to 1 day.
Heat a grill pan over high heat or prepare an outdoor grill for medium-heat cooking. Thread 3 to 4 beef cubes on each skewer, being sure that the tip is covered by beef. Grill, turning occasionally, until beef is browned, 4 to 5 minutes on an outdoor grill and 6 to 7 minutes on a grill pan. Serve the skewers hot with room temperature Romesco sauce.
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