Preheat and prep: Preheat your oven to 400°F (200°C). Trim any silvery membrane from the pork and pat the tenderloin dry with paper towels — drying helps the meat sear and form a flavorful crust rather than steaming.

Season the pork: Rub the pork all over with 1 tbsp olive oil, 1/2 tsp kosher salt, 1/4 tsp black pepper, half the chopped rosemary (1 tsp) and one minced garlic clove. Let it sit at room temperature for 10 minutes while you prep the vegetables — this short rest helps the meat cook more evenly.

Prep the carrots: Toss the baby carrots (or 1" sliced carrots) with 1 tbsp olive oil, 1/4 tsp kosher salt, 1/4 tsp black pepper, the remaining minced garlic (1–2 cloves, finely chopped) and the other 1 tsp chopped rosemary. Spread in a single layer on one side of a rimmed baking sheet (reserve the other half for the pork). Roasting concentrates the carrots' natural sugars and develops a caramelized edge for contrast with the savory pork.

Sear the pork: Heat a 10–12" ovenproof skillet (cast-iron preferred) over medium-high heat until shimmering. Add the pork and sear, undisturbed, 2–3 minutes per side until deeply golden — searing creates Maillard reaction browning that adds flavor and color. If your skillet is dry, add a thin film (½ tsp) of oil, but most of the pork's seasoning oil will suffice.

Roast the pork and carrots together: Transfer the seared pork to the empty side of the baking sheet (or leave it in the skillet and add the carrots to the pan if there’s room). Roast in the preheated oven for 12–16 minutes, or until an instant-read thermometer inserted into the thickest part of the tenderloin reads 140°F (60°C). Because tenderloin is lean, cooking to 140°F will give a slightly pink, juicy center; it will rise a few degrees while resting.

Start the mash while the meat roasts: Bring a medium pot of salted water to a simmer and add the cauliflower florets. Simmer for 8–10 minutes until very tender (a knife should slide through easily). Cooking the cauliflower until soft ensures the mash will be silky without lumps.

Finish the pork and rest: Remove the pork from the oven and transfer to a cutting board. Tent loosely with foil and rest for 8–10 minutes — resting allows juices to redistribute so the slices stay moist when cut. While the pork rests, return any pan drippings to the ovenproof skillet over medium heat (or use the baking sheet). Add the reserved chicken stock (1/4 cup) and scrape up the browned bits to create a quick pan sauce; simmer 1–2 minutes to reduce slightly, then stir in a pat (1 tsp) of butter for gloss and seasoning. Taste and adjust salt and pepper.

Drain and mash the cauliflower: Drain the cooked cauliflower well to avoid watery mash. Place in a food processor or high-speed blender with the butter (2 tbsp) and 2–3 tbsp of the reserved warm chicken stock (or hot water) and process until very smooth. You can also mash by hand with a potato masher for a coarser texture. Season with the remaining 1/4 tsp kosher salt and a pinch of pepper. The stock and butter add silkiness and a savory depth without making the mash heavy.

Finish the carrots: If the carrots are nicely caramelized after roasting, leave them as-is; if they need additional color, place them under the broiler 1–2 minutes. Toss briefly with a small knob of butter (1 tsp) or a drizzle of olive oil and a sprinkle of fresh rosemary for shine and aroma.

Slice and plate: Slice the rested pork tenderloin into 1/2" medallions (slice against the grain for maximum tenderness). Spoon a generous mound of mashed cauliflower onto each plate, arrange the roasted carrots alongside, and fan the pork medallions over the mash. Spoon the pan sauce over the pork and finish with a light scattering of fresh rosemary and a grind of black pepper. Serve immediately.