Add the water, brown sugar, maple syrup, salt, apple cider vinegar, sage, rosemary, peppercorns, and mustard seeds to a large pot. Cook over medium-high heat until the mixture begins to boil. Once the mixture has been boiling for a few minutes and the sugar and salt are completely dissolved, remove from heat and let cool completely. If you want the brine to cool more quickly, you can stick it in the fridge, but not directly after it has been on the stove. I would not recommend cooling it with ice cubes as it may dilute the flavor.
Sage and rosemary, 5 cups water, 2 tablespoons dark brown sugar, ½ cup maple syrup, ¼ cup kosher salt, ½ cup apple cider vinegar, 12 sage leaves, 2 sprigs of rosemary, 2 tablespoons black peppercorns, 2 tablespoons mustard seed
Add the brine and pork to a large marinating bag or a large bowl. You want the pork to be completely submerged. Transfer to a refrigerator and let the tenderloin sit in the brine for 1-2 hours.
2 pounds pork tenderloin
While the tenderloin is brining, make the maple glaze by whisking together maple syrup, dijon mustard, and apple cider vinegar in a small bowl and set aside.
3 tablespoons maple syrup, 3 tablespoons Dijon mustard, 3 tablespoons apple cider vinegar
Preheat your oven to 350 °F (177 °C)
Once the pork is done brining, rinse with water and pat dry.
Heat oil in a cast iron skillet over medium high heat. Add the pork to the skillet and brown the meat for 2 minutes on each side. Brush the maple glaze over the browned pork tenderloin. Do not use all of it. Reserve any leftover glaze to use for the pan sauce.
Transfer the pork tenderloin to the oven to finish cooking. Roast for 25 minutes or until the tenderloin reaches an internal temperature of 145 °F (63 °C)
Remove from the oven and transfer the tenderloin to a cutting board to rest for at least 10 minutes.
While the pork is resting, make the pan sauce. Add the remaining glaze, 1 tablespoon (14g) of butter, and 2 sage leaves to the skillet with the pork’s rendered juice. Let the butter melt and stir the ingredients to create a decadent pan sauce. Spoon this over the pork when you are ready to serve.