Preheat oven to 475°F. Pat the pork tenderloin dry and season on all sides with salt and pepper.
3 lb pork tenderloin, 1 tsp kosher salt, ½ tsp black pepper
In a small saucepan over medium heat, melt 2 tablespoon butter.
2 tbsp unsalted butter
Add garlic and shallot, sauté 1–2 minutes until fragrant.
2 cloves garlic, 2 tbsp shallot
Stir in tomato paste, mustard, honey, apple butter, red wine vinegar, and thyme.
1 tbsp tomato paste, 2 tbsp whole grain mustard, 1 tbsp honey, 3 tbsp apple butter, 2 tbsp red wine vinegar, 1 tsp chopped fresh thyme
Simmer for 5–7 minutes, stirring occasionally, until thickened.
Add salt and pepper. Taste and adjust: add a splash more vinegar for brightness or apple butter for sweetness.
½ teaspoon salt, ½ teaspoon coarse ground pepper
Reserve about ¼ cup in a small bowl for brushing during roasting. Keep the rest warm for serving.
Sear the pork: Heat a large oven-proof skillet over medium-high heat for 2 minutes. Add olive oil and swirl to coat. Place pork in skillet and sear: 2 minutes per side for the first two sides, then 1 minute each for the remaining two sides (total 6 minutes).
1 tbsp olive oil
Remove skillet from heat. Brush pork with half of the reserved apple butter glaze.
Transfer skillet to the oven and roast for 10 minutes.
Flip pork, brush with remaining reserved glaze, and roast another 8–10 minutes, or until an instant-read thermometer in the thickest part registers 140°F.
Remove from oven and let pork rest on a cutting board for 10 minutes.
Slice pork tenderloin and drizzle with the warm apple butter sauce. Garnish with thyme sprigs if desired.
Fresh thyme sprigs