Chop onions into half moon strips.
In a pan, add onions and pour in enough water to fill about 1/4 inch depth.
Cover with a lid and turn the heat on high. Steam for about 10 minutes until the onion is softened.
Add butter and patis.
Lower the heat to medium high and continue cooking with the lid off. Push around the onions and allow all the moisture to evaporate.
Once all the liquid is evaporated, spread the onions out evenly and stir less frequently, allowing the onions to brown on the pan. Only stir to prevent burning, about every 2 minutes, for 20-30 minutes.
Deglaze the pan with water as needed until the caramelized onions turn nicely brown. You can stop cooking at light brown, or if you have the time, continue to caramelize them until they reach a deeper shade.
