Preheat the oven to 450°F. Line a rimmed baking sheet with aluminum foil for easy clean up. Prepare the garlic herb butter (below).
Unwrap the 2 pound pork tenderloin and pat dry with paper towels. Set on the prepared baking sheet and set aside.
In a small bowl, combine the 1 teaspoon coarse kosher salt, 1 teaspoon garlic powder, 1 teaspoon onion powder, 1/2 teaspoon freshly ground black pepper and 1/2 teaspoon smoked paprika. Rub both tenderloins with the rub mixture.
Place the pork into the oven, cooking at 450°F for 5 minutes, then reducing the oven temperature to 350°F. Continue to roast for 15 minutes. Baste with a tablespoon of the butter mixture and then return to the oven for 5 minutes.
Remove from the oven and allow to rest for 5-8 minutes.
On a cutting board, cut into 1-inch slices. Serve over mashed potatoes, smothering with additional herb garlic butter.
Herb Garlic Butter:
In a small saucepan, melt the 1 cup unsalted butter over low heat, being careful to just melt, not brown.
When melted stir in the minced 4-6 cloves fresh garlic, minced 1 shallot, chopped 1 tablespoons fresh sage, 1 tablespoon fresh thyme leaves, 1 tablespoon flat parsley, 1 tablespoon fresh rosemary, zest and juice from one lemon, 2 teaspoons worcestershire sauce , 1/2 teaspoon coarse kosher salt and 1/4 teaspoon ground white pepper. Continue to cook on the lowest heat possible, stirring every few minutes.
Keep on low until ready to baste and after basting and using to spoon over the pork when serving.