Cut the ends of the plantain and make a vertical line on opposite sides and peel. Cut into circles that are about 1 ½ inch thick.
In a medium pan add your oil. Fry for 3 ½ minutes on each side over medium heat.
Now add your fried plantains to your mortar and with the aid of the pestle start mashing. Do this for about 2 minutes and you will start seeing the plantain getting smooth.
Add your adobo and garlic and mash for another minute. Finally add your butter and mash for another minute. Serve right away and enjoy.
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Notes
Your plantains should be green but if yours are starting to change color into a light yellow you can still make it but it will have a sweet taste it won't have that authentic flavor.
The size of the plantains can change how seasoned the mofongo tastes. Make sure that after you add your seasoning and mash the plantains you taste it to see if it needs more.
Make sure your butter is at room temperature. The reason for this is that if you use cold butter it will make your mofongo cold.
To serve you can leave the mofongo in the mortar or just flip it onto a plate. You can use a small bowl or dish to shape it.