In a food processor, chop onion for aobut 10-15 seconds. Empty onto a cheese cloth or tea towel. Squeeze the juice out of the onion and return onion to processor.
Add ground lamb, garlic, marjoram, rosemary, salt, and pepper and process until it is a fine paste – about a minute.
Preheat oven to 325°F. Place mixture into a loaf pan. Place loaf pan in a water bath and wrap brick in tin foil and bake for 60-75 minutes. Make sure the temp reaches 165°F. Take load out of pan and place brick wrapped in foil on top of the loaf pan and let sit for 15-20 minutes, allowing temp to reach 175°F.