Set the temperature of your Sous Vide Cooker to 185ºF (85ºC).
Place asparagus in a vacuum seal bag. Add the butter and a pinch of salt. Seal the bag using a vacuum sealer on the dry setting.
Place the bag in the preheated water bath and set a timer for 10 to 12 minutes, depending on the thickness of the asparagus.
Remove the bag from the water bath when your timer goes off. Carefully open the bag and remove the asparagus spears, arrange on a serving plate. Spoon some of the butter from the bag over the spears. Garnish with sea salt and mint leaves.