Adjust your oven rack to the middle position and preheat your oven to 450. Line a baking sheet with foil and set a wire rack on top of it.
Rinse and pat dry the pork tenderloin. Season with fresh cracked black pepper and overlay with thyme. Then wrap tenderloin in prosciutto.
Heat 2 tblsp oil over medium heat in a skillet or braiser. Brown each side of your tenderloin, approximately 5-7 minutes per side. Transfer meat to wire rack set in foil lined baking sheet. Bake until meat registers 145 degrees, approximately 15-18 minutes.
Meanwhile, deglaze pan used to brown tenderloin by pouring in the chicken stock. Bring to a simmer. Then whisk in the flour until sauce begins to thicken. Whisk in garlic, thyme, and lemon juice. Cook until sauce is desired thickness, whisking often (approx. 5-10 minutes). Off heat, stir in the chives and a dash of salt & pepper.
Allow tenderloin to stand for a few minutes before slicing. Serve topped with pan sauce.