Melt the butter in a medium sized saucepan, add the onions and stir them into the butter.
Put a lid on the saucepan and turn the heat to medium low for 20 minutes, stirring occasionally.
Take off the lid and cook for another 10 minutes to allow some of the liquid to evaporate.
Add the onions to a blender and pulse them a few times to get to your preferred consistency.
Add the béchamel to the onions and combine.
Check the seasoning and serve.
Notes
Disclaimer:The nutritional information provided is approximate and is calculated using online tools. Information can vary depending on various factors, but we have endeavoured to be as accurate as possible.