• In a large mixing bowl, dissolve the kosher salt, baking soda, and brown sugar in 4 cups of room temperature water. Stir in the peppercorns. This mixture will help tenderize the turkey and infuse it with flavors.
• Submerge the turkey tenderloin fully in the brine solution. Cover and refrigerate for at least 1 hour, but not more than 4 hours to prevent the meat from becoming too salty. This step is crucial for ensuring a juicy and flavorful turkey.
• Remove the tenderloin from the brine, rinse with cool water, pat it dry, and discard the brine.

In The Oven

• Preheat oven to 375°F (190°C) and lightly grease a baking dish.
• In a small bowl, whisk together the mustard, honey, soy sauce, lemon juice, garlic, salt, and pepper.
• Place the turkey tenderloin in the prepared baking dish and pour the sauce over it, turning to coat well. Sprinkle the rosemary and thyme over the turkey and tuck some under the meat and set aside for 15 minutes to absorb the flavors.
• Transfer the baking dish into the preheated oven. Bake the turkey for 35 to 40 minutes. It's important to check the doneness of the turkey by using a meat thermometer. The internal temperature should reach 160°F (68°C to 71°C). The tenderloin will continue to cook as it rests.
• After baking, remove the turkey from the oven and let it rest for 10 minutes or until it reaches an internal temperature of 165°F (74°C) to ensure it's cooked through and safe to eat. This resting period allows the juices to redistribute throughout the meat, making it more tender and flavorful when you slice it.

Slow Cooker

• Place the turkey in the slow cooker. Pour the sauce over the turkey, ensuring it is evenly coated. Cover the slow cooker. Set the slow cooker to low and cook for 3-4 hours, or until the turkey reaches 165°F (74°C).