Fill a medium-sized container or pot with water, attach the sous vide precision cooker and set the temperature to 123ºF/51ºC. (Or 130°F/54ºC for a firmer texture).
Remove the tough muscle from the side of the scallops if attached.
Lightly season the scallops with salt, pepper, and 1 tablespoon olive oil.
Place scallops in one single layer in a large resealable bag or vacuum seal bag. (Make sure to arrange in one layer. If your bag is not large enough, use multiple bags).
Seal the bag using the “water displacement” technique or a vacuum sealer.
Once the temperature has reached the target temperature, place the sealed bag in the water bath and set the timer for 30 minutes. Make sure to submerge the scallops completely in the water.
When the time goes off, transfer the bag to an ice bath. Leave for 15 minutes (or you can chill them in the refrigerator for about 1 hour).
When the scallops are chilled, remove from the bag and pat very dry with paper towels (wet scallops won’t sear properly).
In a large skillet over medium-high heat, add the remaining 1 tablespoon olive oil and 1 tablespoon butter.
When butter stops foaming, add scallops and fry for 30 seconds on one side (until a golden crust forms underneath), then flip and fry again for another 30 seconds until lightly browned. Remove from skillet and transfer to a plate.
Add the remaining 1 tablespoon butter and garlic in the same skillet. Cook for about 1 minute until fragrant.
Add in lemon juice and scrapping up any browned bits. Simmer the sauce for about 2 minutes.
Remove the skillet from the heat and add cooked scallop back into the pan and toss with the sauce.
Garnish with parsley if desired.