In a bowl, whisk together olive oil, soy sauce, Worcestershire sauce, Dijon mustard, brown sugar, apple cider vinegar, orange juice, lemon juice, garlic, onion powder, smoked paprika, thyme, rosemary, salt, pepper, and red pepper flakes (if using).

Place the pork roast in a large zip-top bag or nonreactive container. Pour marinade over the pork, seal, and refrigerate for 8 to 16 hours, turning once if possible.

Remove roast from the fridge 30 to 45 minutes before cooking. Preheat oven to 325°F.

Remove pork from marinade and discard used marinade. Pat roast very dry with paper towels.

Melt butter in a large oven-safe skillet over medium-high heat. Sear roast 2 to 3 minutes per side until browned.

Transfer skillet to the oven and roast until the thickest part reaches 145°F, about 60 to 90 minutes depending on thickness.

Move roast to a cutting board and rest 15 to 20 minutes, tented loosely with foil.

For pan sauce, place skillet on the stove over medium heat. Add chicken broth and scrape up browned bits. Simmer 3 to 5 minutes. For thicker sauce, whisk cornstarch with cold water and whisk into sauce; cook 1 to 2 minutes until glossy.

Slice pork against the grain and serve with sauce and chopped parsley if desired.