The Best Way To Reheat Crispy Brussels Sprouts Is Wonderfully Simple - Tasting Table
Briefly

If you take the time to make delicious Brussels sprouts, it's worth learning how to prepare whatever's left the next day so they're just as tasty.
The secret is to use the same process you did to roast them in the first place: Pop them back in the oven at a lower temperature.
It might be tempting to pop your Brussels sprouts in the microwave, but it won't save you much time compared to just 10 or so minutes in the oven.
If for any reason you can't use the oven, the air fryer is a better bet than the microwave for reheating Brussels sprouts.
Read at Tasting Table
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