My brother is a missionary in Columbia and he is the one who introduced me to mantecadas. They are quite common where they live and they enjoy them just like I like eating a warm muffin.
When my brother and his wife were back in the states, this is one of the things we made together. One tip they gave me is to make sure you add the eggs one at a time and stir well after each egg is added.
For some reason this helps keep the texture lighter. They like making their mantecadas with some vanilla extract and a little bit of cinnamon. This was the perfect complement to my morning cup of hot tea.