Pulse the onion in a food processor for 10 to 15 seconds then put it into the center of a paper towel and squeeze until almost all of the juice is removed; discard juice.
Return the onion to the food processor, add the remaining ingredients, and process until it is a fine paste, approximately 1 minute.
Place the mixture into a loaf pan, making sure to press into the sides of the pan then place the loaf pan into a water bath and bake for 60 to 75 minutes.