Look for fresh scallops that are labeled as dry-packed, which are not treated with preservatives and have a lower water content than wet or "soaked" scallops. Seasoning scallops just before cooking also ensures that they stay dry.
Preheat oven to 500 degrees. Whisk together lemon zest, juice, mustard, and sugar. Stream in olive oil and season with salt and pepper. Add celery, parsley, and raisins. Toss to combine. Season again with salt and pepper.
Heat a medium skillet over high and swirl in safflower oil. When oil shimmers, season scallops with salt, then sear, larger side down, in a single layer. Cook without moving, until underside is golden and a crust has formed, 2 minutes. Add butter and thyme and transfer to the oven. Cook 1 to 2 minutes more. Serve scallops, seared-side up, drizzled with pan juices, alongside celery salad.