Step 1

Place sliced onions into large slow cooker. Add melted butter.

Step 2

Cover and cook on low for 9 hours. Stir every 2-3 hours.

Step 3

Crack the lid to allow liquid to evaporate. Increase heat to high and cook 2 hours or until liquid is evaporated. Stir more frequently during this time.

Step 4

Add salt and sugar the last 10 minutes.

Step 5

Transfer to airtight container using slotted spoon. Refrigerate.