Remove the meat mixture from the fridge and bring to room temperature. Heat a 1/4-inch depth of oil in a cast-iron skillet or large saute pan over med-heat. Test the oil by dropping a tiny piece of the meat mixture into the pan. If it sizzles immediately, the oil is ready; if it burns immediately, the oil is too hot. Carefully drop 1-inch-sized balls of the meat mixture into the oil and fry in batches, making sure not to over-crowd the pan. Using a heatproof rubber spatula or metal implement, carefully turn the balls so they brown evenly, 1-2 minutes on each side. Transfer browned balls to the slow cooker using a metal slotted spoon or spider. Once all the balls are in the slow cooker, cover and cook on the low setting for 2 hours. The slow cooker can remain on the keep warm setting throughout your party, and the balls can be served directly from it. For an authentic flair, serve the meatballs in earthenware casuelitas, or decorative enamel-coated ceramic ramekins, and set out plastic forks or decorative wooden toothpicks. Note: Turn this tapa into an easy meal by serving over peeled, chopped, potatoes boiled 30 minutes in salted water.