Place the butter in a skillet and heat it on medium low, cooking 5-10 minutes until the butter has turned a light to medium brown color. Set aside to cool.
Cut the ends off the parsnips and peel them using a vegetable peel.
Cut them in quarters, lengthwise, so they caramelize evenly.
Place them in a vacuum seal bag with remaining ingredients (including browned butter) and cook for 2 hours.
Heat a skillet over medium high heat and add the parsnips (along with butter in the bag).
Brown on each side, about 1-3 minutes per side and serve with any butter left from the pan on top.
Notes
I recommend using the water displacement method as the parsnips will float and it's easier to release excess air from the bag using this method.
If the bag starts to float, open the top slightly and let excess air out. You can also weigh it down with these sous vide magnets that I really like for dishes like this.
Watch the brown butter as it cooks to make sure it doesn't burn.
If you have limited time, you can also just use regular butter and skip the browning part - the results will still be good.