In a medium saucepan, warm your butter and oil to 220° using a deep fry or candy thermometer.
Gently toss in your shallots, working to separate the rings. Your heat will dip down a bit but heat it back up.
Adjust heat to keep your shallots cooking between 220° and 260°, stirring to keep rings cooking evenly and prevent clumping. Be careful to not let it go above 260° or the onions will brown and burn quickly.
Your onions should take about 35 minutes to evenly cook and turn golden brown. Using a mesh strainer, lift onions out of oil to cool on paper towel lined rack or pan.
Once cool to the touch, store at room temperature in an airtight container for up to a week.
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