Fill large pot or other large, heat-resistant container with water. Insert sous vide immersion circulator and set temperature to 146.5° Fahrenheit. Note: pot must be deep enough that water level falls between minimum and maximum indicators on circulator.
Place 2 medium boneless, skinless chicken breasts on cutting board. Brush or rub 2 teaspoons olive oil evenly over all sides of chicken breasts, then liberally season chicken with salt and freshly cracked black pepper on all sides.
Place chicken in large sealable food-safe bag. Add 2-4 sprigs fresh herb(s) of choice and 1-2 cloves garlic, then remove as much air as possible from bag using vacuum sealer or water displacement method (see Notes). Seal bag completely.
Once water bath is preheated to 146.5° Fahrenheit, place sealed bag in water bath. Make sure chicken breasts are fully submerged in water. If needed, use sous vide weights, silverware, or pie weights to keep chicken completely submerged.
Cook chicken breasts 1 hour. Toward end of 1-hour cook time, heat skillet over medium-high heat. When pan is warm, add 2 tablespoons unsalted butter. Swirl and tilt pan to distribute butter across surface, letting butter melt completely.
While butter melts, remove bag from water bath. Transfer chicken breasts to large plate and pat chicken completely dry on all sides with paper towels.
Once butter begins to foam, place chicken breasts in skillet. Sear chicken 1 minute, then flip chicken over and sear 1 additional minute or until chicken is browned on both sides.
Plate seared chicken with desired sides and serve warm.