Start by removing the spatchcocked chicken from its packaging. Use paper towels to blot it dry. This is an important step to ensure the skin gets crispy later.
With two fingers, gently separate the skin from the meat on the breast, legs, and back. Be careful not to tear the skin; this will allow the garlic butter mixture to infuse flavor directly into the meat.
Place the chicken in a roasting pan and liberally sprinkle the entire exterior with 1 tablespoon of coarse kosher salt. If you have time, you can do this the day before and let it sit uncovered in the fridge overnight for a dry brine.
While waiting for the water to heat, fill your sous vide container with water and set the machine to 145° F. This process can take about 30 minutes, depending on the initial temperature of the water.
In a small bowl, combine the softened butter, minced garlic, lemon zest, chopped rosemary, chopped thyme, black pepper, and remaining salt. Mix until well combined.
Using your fingers, spread the garlic butter mixture evenly under the skin and all over the skin of the chicken. Make sure to cover it thoroughly for maximum flavor.
Place some of the lemon slices inside the chicken breasts and thighs, as this adds moisture and flavor from the inside out.
Carefully place the whole chicken into a vacuum seal bag, sealing it on one side.
Next, place the remaining lemon slices along with a few sprigs of the rosemary and thyme around the chicken inside the bag.
Once your water has reached the set temperature, immerse the vacuum-sealed chicken in the container, ensuring it is completely submerged. Set the timer for 5 hours.
Preheat your oven to 450° F. This will give you a crispy skin once the sous vide cooking is complete.
After 5 hours, carefully remove the chicken from the sous vide bag. Reserve the liquid for later use, or discard if you prefer. Discard the lemons and larger pieces of herbs from the chicken.
Transfer the chicken into a roasting dish and bake for 30 to 40 minutes, or until the internal temperature reaches 165° F, and the skin is beautifully browned and crispy. If the skin isn’t fully browned but is at the right temperature, turn on the broiler for a minute or two, watching closely to prevent burning.
Once cooked, remove the chicken from the oven and let it rest for 10 minutes before carving and serving. This resting period is crucial for the juices to redistribute for maximum tenderness.
