Place butter in med. saucepan w/ pouring lip. Add remaining ingredients. Bring to low simmer over med.-low heat, stirring occasionally.
Reduce heat to low. Continue cooking, stirring frequently, 60-90 min. Do not let the butter burn.
Remove from heat. Rest 1-2 min.
Meanwhile, line strainer w/ 3-4 layers of cheesecloth. Remove lg pieces of onion and herbs w/ slotted spoon and discard. Pour butter through strainer into heat-safe measuring cup or mixing bowl w/ pouring lip.
Let cool. Transfer to clean, dry jar and seal. Niter Kibbeh should keep 4-5 weeks in pantry, or 2-3 months in refrigerator.