Inexpensive family owned Nonna Bianca in San Telmo on Estados Unidos 425 (betw Defensa and Bolivar) is my favorite ice-cream spot. Their specialty is homemade Italian-style gelato. There is about 80 flavors on offer, some of them quite exotic like kumquats soaked in whiskey! They are open every day till late and serve coffee, milkshakes, pastries, quiches and other snacks besides the ice cream.