Season pork with salt. Let sit 15 minutes while you prepare the marinade.

Combine wine, brown sugar, vinegar, garlic, bay leaves, oregano, and 1/4 cup oil in a large resealable plastic bag. Add pork, seal tightly, pressing as much air out of bag as possible, and turn to coat. Chill at least 2 hours or up to overnight.

Place a rack in center of oven; preheat to 325°. Remove pork from marinade and pat dry; reserve marinade. Heat remaining 1 Tbsp. oil in a 12″ skillet over medium-high. Cook pork, turning occasionally, until golden brown all over, 6-8 minutes.

Remove pan from heat and let cool 1 minute. Pour reserved marinade over pork. Transfer pan to oven and bake, turning pork over once in its sauce halfway through, until an instant-read thermometer inserted into the thickest part of tenderloin registers 145°, 22-26 minutes, depending on thickness.

Transfer pork to a cutting board and let rest 10 minutes. Return pan to medium-high heat. Add butter and cook, swirling pan occasionally, until slightly reduced. 3-5 minutes. Stir in parsley.

Slice tenderloin crosswise against the grain. Transfer to a platter and spoon pan sauce over.

Serve with al dente angel hair pasta (optional).