Preheat your cast-iron skillet over medium-high heat until it’s shimmering and hot, about 3-4 minutes, with a gentle sizzle when you flick a drop of water.
In the meantime, pat the salmon fillets dry with paper towels to remove excess moisture, which helps the crust stick and sear evenly.
In a small bowl, combine smoked paprika, cayenne pepper, black pepper, sea salt, and dried thyme if using. Stir until well blended to create your spice rub.
Lightly brush each salmon fillet on all sides with the high-smoke point oil, ensuring an even coat to help the spices adhere and prevent sticking.
Press the spice mixture firmly onto all sides of each fillet, creating a thick, even crust that covers the surface thoroughly.
Place the coated salmon fillets skin-side down (if skin-on) in the hot skillet. Gently press down with a spatula for about 10 seconds to ensure good contact and crust formation.
Sear for 3-4 minutes, until the crust is darkened and aromatic with a crackling sound, indicating a good sear.
Carefully flip each fillet using a spatula and cook for another 2-3 minutes, watching for a deep, smoky crust and an internal temperature of about 52°C (125°F).
Remove the salmon from the skillet and transfer to a plate. Let it rest for 2 minutes, allowing the juices to settle and the crust to crisp up further.
Squeeze fresh lemon juice over the rested salmon just before serving to brighten the smoky flavors and add a zesty finish.
Serve immediately with your favorite sides, enjoying the fiery crust and tender, flaky flesh of the salmon.
