How to Make It
Preheat the oven to 450°. On a large rimmed baking sheet, toss the potatoes and thyme sprigs with 3 tablespoons of the olive oil and season with salt and pepper. Roast for 10 minutes, until just starting to brown.
On a work surface, brush the pork all over with olive oil and season with salt and pepper. Drizzle the grapes and garlic with the remaining 1 tablespoon of olive oil and season with salt and pepper. Add the pork, grapes and garlic to the baking sheet with the potatoes. Roast for 20 to 25 minutes, until an instant-read thermometer inserted in the thickest part of the pork registers 135°.
Transfer the pork to a work surface and let rest for 10 minutes, then slice against the grain. Transfer the pork, fingerlings, grapes and garlic to a platter and serve.