Start your water bath. Set it to 183 degrees for 30 minutes or 45 minutes if you want softer vegetables.
Add veggies and cold butter to a sous vide bag. Add salt and pepper to taste. If using dill or fennel seed add that now too.
Try to get the vegetables as flat as you can in a single layer and then seal with a vacuum sealer. If you don't have one use the water displacement method.
Add to water bath once it has recached temperature. If the bag floats, use something heavy like a small pot to keep it submerged. Make sure you don't pass the max fill line for your sous vide machine.
Remove veggies from water bath when done with a pair of tongs. Serve immediately.